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 $75.59   11.184%   $84.044   $84.04   $84.05   $84.00  
  Purchase #2 $216.46   9.157%   $236.2812   $236.28   $236.30   $236.30  
  Purchase #3 $95.47   9.579%   $104.6151   $104.62   $104.60   $104.60  
  Purchase #4 $97.33   5.248%   $102.4379   $102.44   $102.45   $102.40  
  Purchase #5 $237.62   12.601%   $267.5625   $267.56   $267.55   $267.60  
  Purchase #6 $167.54   9.742%   $183.8617   $183.86   $183.85   $183.90  
  Purchase #7 $232.65   10.348%   $256.7246   $256.72   $256.70   $256.70  
  7 purchase totals = $1,122.66       $1,235.5270   $1,235.52   $1,235.50   $1,235.50