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 $79.49   10.718%   $88.0097   $88.01   $88.00   $88.00  
  Purchase #2 $189.83   4.124%   $197.6586   $197.66   $197.65   $197.70  
  Purchase #3 $7.95   3.691%   $8.2434   $8.24   $8.25   $8.20  
  Purchase #4 $170.64   3.577%   $176.7438   $176.74   $176.75   $176.70  
  Purchase #5 $85.66   11.699%   $95.6814   $95.68   $95.70   $95.70  
  Purchase #6 $32.55   11.528%   $36.3024   $36.30   $36.30   $36.30  
  Purchase #7 $151.69   9.515%   $166.1233   $166.12   $166.10   $166.10  
  7 purchase totals = $717.81       $768.7626   $768.75   $768.75   $768.70