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 $168.55   13.601%   $191.4745   $191.47   $191.45   $191.50  
  Purchase #2 $146.97   8.505%   $159.4698   $159.47   $159.45   $159.50  
  Purchase #3 $46.67   9.478%   $51.0934   $51.09   $51.10   $51.10  
  Purchase #4 $109.93   12.764%   $123.9615   $123.96   $123.95   $124.00  
  Purchase #5 $185.79   13.595%   $211.0482   $211.05   $211.05   $211.00  
  Purchase #6 $187.71   3.168%   $193.6567   $193.66   $193.65   $193.70  
  Purchase #7 $10.95   12.464%   $12.3148   $12.31   $12.30   $12.30  
  7 purchase totals = $856.57       $943.0189   $943.01   $942.95   $943.10