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 $185.39   12.430%   $208.434   $208.43   $208.45   $208.40  
  Purchase #2 $231.59   6.230%   $246.0181   $246.02   $246.00   $246.00  
  Purchase #3 $175.74   10.573%   $194.321   $194.32   $194.30   $194.30  
  Purchase #4 $91.82   7.776%   $98.9599   $98.96   $98.95   $99.00  
  Purchase #5 $173.79   11.572%   $193.901   $193.90   $193.90   $193.90  
  Purchase #6 $232.62   9.465%   $254.6375   $254.64   $254.65   $254.60  
  Purchase #7 $35.68   11.181%   $39.6694   $39.67   $39.65   $39.70  
  7 purchase totals = $1,126.63       $1,235.9409   $1,235.94   $1,235.90   $1,235.90