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 $204.47   6.498%   $217.7565   $217.76   $217.75   $217.80  
  Purchase #2 $106.25   6.676%   $113.3433   $113.34   $113.35   $113.30  
  Purchase #3 $11.50   9.858%   $12.6337   $12.63   $12.65   $12.60  
  Purchase #4 $232.81   7.267%   $249.7283   $249.73   $249.75   $249.70  
  Purchase #5 $60.76   10.328%   $67.0353   $67.04   $67.05   $67.00  
  Purchase #6 $226.60   9.259%   $247.5809   $247.58   $247.60   $247.60  
  Purchase #7 $201.84   12.464%   $226.9973   $227.00   $227.00   $227.00  
  7 purchase totals = $1,044.23       $1,135.0753   $1,135.08   $1,135.15   $1,135.00