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 $53.72   5.655%   $56.7579   $56.76   $56.75   $56.80  
  Purchase #2 $214.80   3.212%   $221.6994   $221.70   $221.70   $221.70  
  Purchase #3 $156.96   8.862%   $170.8698   $170.87   $170.85   $170.90  
  Purchase #4 $58.72   10.319%   $64.7793   $64.78   $64.80   $64.80  
  Purchase #5 $243.31   12.182%   $272.95   $272.95   $272.95   $273.00  
  Purchase #6 $42.54   4.231%   $44.3399   $44.34   $44.35   $44.30  
  Purchase #7 $13.93   7.301%   $14.947   $14.95   $14.95   $14.90  
  7 purchase totals = $783.98       $846.3433   $846.35   $846.35   $846.40