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 $198.85   13.466%   $225.6271   $225.63   $225.65   $225.60  
  Purchase #2 $182.77   10.417%   $201.8092   $201.81   $201.80   $201.80  
  Purchase #3 $84.46   12.407%   $94.939   $94.94   $94.95   $94.90  
  Purchase #4 $5.50   13.736%   $6.2555   $6.26   $6.25   $6.30  
  Purchase #5 $249.30   5.331%   $262.5902   $262.59   $262.60   $262.60  
  Purchase #6 $42.72   4.513%   $44.648   $44.65   $44.65   $44.60  
  Purchase #7 $107.55   11.330%   $119.7354   $119.74   $119.75   $119.70  
  7 purchase totals = $871.15       $955.6044   $955.62   $955.65   $955.50