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 $58.92   4.568%   $61.6115   $61.61   $61.60   $61.60  
  Purchase #2 $139.39   8.304%   $150.9649   $150.96   $150.95   $151.00  
  Purchase #3 $109.76   13.278%   $124.3339   $124.33   $124.35   $124.30  
  Purchase #4 $236.93   5.530%   $250.0322   $250.03   $250.05   $250.00  
  Purchase #5 $109.81   13.649%   $124.798   $124.80   $124.80   $124.80  
  Purchase #6 $141.44   11.757%   $158.0691   $158.07   $158.05   $158.10  
  Purchase #7 $126.29   9.598%   $138.4113   $138.41   $138.40   $138.40  
  7 purchase totals = $922.54       $1,008.2209   $1,008.21   $1,008.20   $1,008.20