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 $71.25   6.579%   $75.9375   $75.94   $75.95   $75.90  
  Purchase #2 $53.96   8.335%   $58.4576   $58.46   $58.45   $58.50  
  Purchase #3 $81.63   11.440%   $90.9685   $90.97   $90.95   $91.00  
  Purchase #4 $186.88   7.735%   $201.3352   $201.34   $201.35   $201.30  
  Purchase #5 $177.84   10.725%   $196.9133   $196.91   $196.90   $196.90  
  Purchase #6 $179.92   7.390%   $193.2161   $193.22   $193.20   $193.20  
  Purchase #7 $54.42   5.380%   $57.3478   $57.35   $57.35   $57.30  
  7 purchase totals = $805.90       $874.1760   $874.19   $874.15   $874.10