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 $15.39   4.858%   $16.1376   $16.14   $16.15   $16.10  
  Purchase #2 $190.76   6.650%   $203.4455   $203.45   $203.45   $203.40  
  Purchase #3 $55.80   7.570%   $60.0241   $60.02   $60.00   $60.00  
  Purchase #4 $141.38   5.754%   $149.515   $149.52   $149.50   $149.50  
  Purchase #5 $219.32   6.257%   $233.0429   $233.04   $233.05   $233.00  
  Purchase #6 $248.65   5.532%   $262.4053   $262.41   $262.40   $262.40  
  Purchase #7 $18.75   5.235%   $19.7316   $19.73   $19.75   $19.70  
  7 purchase totals = $890.05       $944.3020   $944.31   $944.30   $944.10