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 $40.49   6.311%   $43.0453   $43.05   $43.05   $43.00  
  Purchase #2 $183.75   12.353%   $206.4486   $206.45   $206.45   $206.40  
  Purchase #3 $51.70   3.530%   $53.525   $53.53   $53.55   $53.50  
  Purchase #4 $250.54   4.819%   $262.6135   $262.61   $262.60   $262.60  
  Purchase #5 $5.52   11.694%   $6.1655   $6.17   $6.15   $6.20  
  Purchase #6 $111.77   12.242%   $125.4529   $125.45   $125.45   $125.50  
  Purchase #7 $233.42   12.590%   $262.8076   $262.81   $262.80   $262.80  
  7 purchase totals = $877.19       $960.0584   $960.07   $960.05   $960.00