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 $203.42   12.463%   $228.7722   $228.77   $228.75   $228.80  
  Purchase #2 $244.55   7.395%   $262.6345   $262.63   $262.65   $262.60  
  Purchase #3 $86.48   7.854%   $93.2721   $93.27   $93.25   $93.30  
  Purchase #4 $38.78   8.605%   $42.117   $42.12   $42.10   $42.10  
  Purchase #5 $19.41   10.474%   $21.443   $21.44   $21.45   $21.40  
  Purchase #6 $62.82   10.514%   $69.4249   $69.42   $69.40   $69.40  
  Purchase #7 $219.72   7.492%   $236.1814   $236.18   $236.20   $236.20  
  7 purchase totals = $875.18       $953.8451   $953.83   $953.80   $953.80