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 $91.68   12.181%   $102.8475   $102.85   $102.85   $102.80  
  Purchase #2 $60.27   11.422%   $67.154   $67.15   $67.15   $67.20  
  Purchase #3 $116.85   6.544%   $124.4967   $124.50   $124.50   $124.50  
  Purchase #4 $203.78   11.428%   $227.068   $227.07   $227.05   $227.10  
  Purchase #5 $250.36   6.241%   $265.985   $265.99   $266.00   $266.00  
  Purchase #6 $95.26   8.381%   $103.2437   $103.24   $103.25   $103.20  
  Purchase #7 $209.79   10.869%   $232.5921   $232.59   $232.60   $232.60  
  7 purchase totals = $1,027.99       $1,123.3870   $1,123.39   $1,123.40   $1,123.40