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 $37.86   10.251%   $41.741   $41.74   $41.75   $41.70  
  Purchase #2 $189.34   8.752%   $205.911   $205.91   $205.90   $205.90  
  Purchase #3 $250.52   12.537%   $281.9277   $281.93   $281.95   $281.90  
  Purchase #4 $148.76   6.534%   $158.48   $158.48   $158.50   $158.50  
  Purchase #5 $170.71   4.767%   $178.8477   $178.85   $178.85   $178.80  
  Purchase #6 $155.52   4.800%   $162.985   $162.99   $163.00   $163.00  
  Purchase #7 $12.60   11.297%   $14.0234   $14.02   $14.00   $14.00  
  7 purchase totals = $965.31       $1,043.9158   $1,043.92   $1,043.95   $1,043.80