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 $136.44   11.382%   $151.9696   $151.97   $151.95   $152.00  
  Purchase #2 $114.62   8.647%   $124.5312   $124.53   $124.55   $124.50  
  Purchase #3 $17.34   9.620%   $19.0081   $19.01   $19.00   $19.00  
  Purchase #4 $249.72   11.616%   $278.7275   $278.73   $278.75   $278.70  
  Purchase #5 $24.94   13.514%   $28.3104   $28.31   $28.30   $28.30  
  Purchase #6 $199.28   6.321%   $211.8765   $211.88   $211.90   $211.90  
  Purchase #7 $224.81   6.288%   $238.9461   $238.95   $238.95   $238.90  
  7 purchase totals = $967.15       $1,053.3694   $1,053.38   $1,053.40   $1,053.30