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 $90.33   5.281%   $95.1003   $95.10   $95.10   $95.10  
  Purchase #2 $241.35   10.696%   $267.1648   $267.16   $267.15   $267.20  
  Purchase #3 $45.62   10.363%   $50.3476   $50.35   $50.35   $50.30  
  Purchase #4 $113.44   5.161%   $119.2946   $119.29   $119.30   $119.30  
  Purchase #5 $67.52   5.582%   $71.289   $71.29   $71.30   $71.30  
  Purchase #6 $234.75   9.598%   $257.2813   $257.28   $257.30   $257.30  
  Purchase #7 $110.48   9.605%   $121.0916   $121.09   $121.10   $121.10  
  7 purchase totals = $903.49       $981.5692   $981.56   $981.60   $981.60