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 $126.81   7.563%   $136.4006   $136.40   $136.40   $136.40  
  Purchase #2 $106.85   12.208%   $119.8942   $119.89   $119.90   $119.90  
  Purchase #3 $106.75   11.642%   $119.1778   $119.18   $119.20   $119.20  
  Purchase #4 $64.44   4.726%   $67.4854   $67.49   $67.50   $67.50  
  Purchase #5 $91.57   7.748%   $98.6648   $98.66   $98.65   $98.70  
  Purchase #6 $237.59   4.203%   $247.5759   $247.58   $247.60   $247.60  
  Purchase #7 $135.25   5.576%   $142.7915   $142.79   $142.80   $142.80  
  7 purchase totals = $869.26       $931.9902   $931.99   $932.05   $932.10