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 $112.85   10.681%   $124.9035   $124.90   $124.90   $124.90  
  Purchase #2 $155.31   3.398%   $160.5874   $160.59   $160.60   $160.60  
  Purchase #3 $136.76   4.773%   $143.2876   $143.29   $143.30   $143.30  
  Purchase #4 $86.78   12.180%   $97.3498   $97.35   $97.35   $97.30  
  Purchase #5 $213.35   10.412%   $235.564   $235.56   $235.55   $235.60  
  Purchase #6 $182.54   8.102%   $197.3294   $197.33   $197.35   $197.30  
  Purchase #7 $123.53   3.767%   $128.1834   $128.18   $128.20   $128.20  
  7 purchase totals = $1,011.12       $1,087.2051   $1,087.20   $1,087.25   $1,087.20