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 $189.34   3.511%   $195.9877   $195.99   $196.00   $196.00  
  Purchase #2 $178.53   5.480%   $188.3134   $188.31   $188.30   $188.30  
  Purchase #3 $114.64   10.426%   $126.5924   $126.59   $126.60   $126.60  
  Purchase #4 $52.26   5.508%   $55.1385   $55.14   $55.15   $55.10  
  Purchase #5 $250.51   7.229%   $268.6194   $268.62   $268.60   $268.60  
  Purchase #6 $210.38   8.642%   $228.561   $228.56   $228.55   $228.60  
  Purchase #7 $222.57   4.302%   $232.145   $232.15   $232.15   $232.10  
  7 purchase totals = $1,218.23       $1,295.3574   $1,295.36   $1,295.35   $1,295.30