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 $138.89   13.359%   $157.4443   $157.44   $157.45   $157.40  
  Purchase #2 $239.93   7.501%   $257.9271   $257.93   $257.95   $257.90  
  Purchase #3 $65.45   9.267%   $71.5153   $71.52   $71.50   $71.50  
  Purchase #4 $64.54   13.530%   $73.2723   $73.27   $73.25   $73.30  
  Purchase #5 $95.77   6.188%   $101.6962   $101.70   $101.70   $101.70  
  Purchase #6 $198.57   3.843%   $206.201   $206.20   $206.20   $206.20  
  Purchase #7 $169.56   7.728%   $182.6636   $182.66   $182.65   $182.70  
  7 purchase totals = $972.71       $1,050.7198   $1,050.72   $1,050.70   $1,050.70