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 $68.45   10.473%   $75.6188   $75.62   $75.60   $75.60  
  Purchase #2 $190.72   5.230%   $200.6947   $200.69   $200.70   $200.70  
  Purchase #3 $66.35   10.158%   $73.0898   $73.09   $73.10   $73.10  
  Purchase #4 $51.57   8.143%   $55.7693   $55.77   $55.75   $55.80  
  Purchase #5 $230.27   3.217%   $237.6778   $237.68   $237.70   $237.70  
  Purchase #6 $206.72   13.321%   $234.2572   $234.26   $234.25   $234.30  
  Purchase #7 $131.94   8.644%   $143.3449   $143.34   $143.35   $143.30  
  7 purchase totals = $946.02       $1,020.4525   $1,020.45   $1,020.45   $1,020.50