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 $175.43   11.611%   $195.7992   $195.80   $195.80   $195.80  
  Purchase #2 $153.45   12.776%   $173.0548   $173.05   $173.05   $173.10  
  Purchase #3 $156.79   11.190%   $174.3348   $174.33   $174.35   $174.30  
  Purchase #4 $40.77   8.655%   $44.2986   $44.30   $44.30   $44.30  
  Purchase #5 $199.38   6.105%   $211.5521   $211.55   $211.55   $211.60  
  Purchase #6 $7.87   13.632%   $8.9428   $8.94   $8.95   $8.90  
  Purchase #7 $196.84   8.229%   $213.038   $213.04   $213.05   $213.00  
  7 purchase totals = $930.53       $1,021.0203   $1,021.01   $1,021.05   $1,021.00