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 $240.50   8.550%   $261.0628   $261.06   $261.05   $261.10  
  Purchase #2 $202.82   12.139%   $227.4403   $227.44   $227.45   $227.40  
  Purchase #3 $13.38   4.497%   $13.9817   $13.98   $14.00   $14.00  
  Purchase #4 $168.52   10.726%   $186.5955   $186.60   $186.60   $186.60  
  Purchase #5 $32.33   12.279%   $36.2998   $36.30   $36.30   $36.30  
  Purchase #6 $19.94   11.390%   $22.2112   $22.21   $22.20   $22.20  
  Purchase #7 $209.77   12.795%   $236.6101   $236.61   $236.60   $236.60  
  7 purchase totals = $887.26       $984.2014   $984.20   $984.20   $984.20