Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $121.95   3.869%   $126.6682   $126.67   $126.65   $126.70  
  Purchase #2 $227.48   11.153%   $252.8508   $252.85   $252.85   $252.90  
  Purchase #3 $112.71   12.204%   $126.4651   $126.47   $126.45   $126.50  
  Purchase #4 $172.39   11.275%   $191.827   $191.83   $191.85   $191.80  
  Purchase #5 $105.25   3.586%   $109.0243   $109.02   $109.00   $109.00  
  Purchase #6 $228.46   9.586%   $250.3602   $250.36   $250.35   $250.40  
  Purchase #7 $210.93   13.523%   $239.4541   $239.45   $239.45   $239.50  
  7 purchase totals = $1,179.17       $1,296.6497   $1,296.65   $1,296.60   $1,296.80