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 $66.59   12.166%   $74.6913   $74.69   $74.70   $74.70  
  Purchase #2 $18.33   7.452%   $19.696   $19.70   $19.70   $19.70  
  Purchase #3 $29.34   8.873%   $31.9433   $31.94   $31.95   $31.90  
  Purchase #4 $148.68   10.760%   $164.678   $164.68   $164.70   $164.70  
  Purchase #5 $133.36   13.290%   $151.0835   $151.08   $151.10   $151.10  
  Purchase #6 $66.33   12.112%   $74.3639   $74.36   $74.35   $74.40  
  Purchase #7 $198.80   11.460%   $221.5825   $221.58   $221.60   $221.60  
  7 purchase totals = $661.43       $738.0385   $738.03   $738.10   $738.10