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 $49.76   10.191%   $54.831   $54.83   $54.85   $54.80  
  Purchase #2 $119.51   6.214%   $126.9364   $126.94   $126.95   $126.90  
  Purchase #3 $117.43   4.276%   $122.4513   $122.45   $122.45   $122.50  
  Purchase #4 $204.50   13.365%   $231.8314   $231.83   $231.85   $231.80  
  Purchase #5 $231.31   9.156%   $252.4887   $252.49   $252.50   $252.50  
  Purchase #6 $51.38   13.323%   $58.2254   $58.23   $58.25   $58.20  
  Purchase #7 $98.25   11.706%   $109.7511   $109.75   $109.75   $109.80  
  7 purchase totals = $872.14       $956.5153   $956.52   $956.60   $956.50