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 $60.47   6.246%   $64.247   $64.25   $64.25   $64.20  
  Purchase #2 $136.45   5.760%   $144.3095   $144.31   $144.30   $144.30  
  Purchase #3 $26.71   12.518%   $30.0536   $30.05   $30.05   $30.10  
  Purchase #4 $207.25   11.289%   $230.6465   $230.65   $230.65   $230.60  
  Purchase #5 $219.30   9.613%   $240.3813   $240.38   $240.40   $240.40  
  Purchase #6 $27.49   9.276%   $30.04   $30.04   $30.05   $30.00  
  Purchase #7 $179.52   8.483%   $194.7487   $194.75   $194.75   $194.70  
  7 purchase totals = $857.19       $934.4266   $934.43   $934.45   $934.30