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 $232.73   6.432%   $247.6992   $247.70   $247.70   $247.70  
  Purchase #2 $118.87   5.550%   $125.4673   $125.47   $125.45   $125.50  
  Purchase #3 $62.61   11.107%   $69.5641   $69.56   $69.55   $69.60  
  Purchase #4 $85.66   7.657%   $92.219   $92.22   $92.20   $92.20  
  Purchase #5 $160.57   4.216%   $167.3396   $167.34   $167.35   $167.30  
  Purchase #6 $149.44   6.184%   $158.6814   $158.68   $158.70   $158.70  
  Purchase #7 $141.75   9.201%   $154.7924   $154.79   $154.80   $154.80  
  7 purchase totals = $951.63       $1,015.7630   $1,015.76   $1,015.75   $1,015.80