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 $126.81   7.773%   $136.6669   $136.67   $136.65   $136.70  
  Purchase #2 $171.81   7.494%   $184.6854   $184.69   $184.70   $184.70  
  Purchase #3 $198.49   10.716%   $219.7602   $219.76   $219.75   $219.80  
  Purchase #4 $68.32   8.214%   $73.9318   $73.93   $73.95   $73.90  
  Purchase #5 $183.64   3.461%   $189.9958   $190.00   $190.00   $190.00  
  Purchase #6 $250.75   10.485%   $277.0411   $277.04   $277.05   $277.00  
  Purchase #7 $146.29   5.156%   $153.8327   $153.83   $153.85   $153.80  
  7 purchase totals = $1,146.11       $1,235.9139   $1,235.92   $1,235.95   $1,235.90