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 $205.55   10.535%   $227.2047   $227.20   $227.20   $227.20  
  Purchase #2 $47.74   8.332%   $51.7177   $51.72   $51.70   $51.70  
  Purchase #3 $85.36   3.515%   $88.3604   $88.36   $88.35   $88.40  
  Purchase #4 $220.38   11.218%   $245.1022   $245.10   $245.10   $245.10  
  Purchase #5 $155.68   13.239%   $176.2905   $176.29   $176.30   $176.30  
  Purchase #6 $34.68   5.123%   $36.4567   $36.46   $36.45   $36.50  
  Purchase #7 $186.75   5.342%   $196.7262   $196.73   $196.75   $196.70  
  7 purchase totals = $936.14       $1,021.8584   $1,021.86   $1,021.85   $1,021.90