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 $195.75   6.781%   $209.0238   $209.02   $209.00   $209.00  
  Purchase #2 $50.64   7.734%   $54.5565   $54.56   $54.55   $54.60  
  Purchase #3 $83.80   11.725%   $93.6256   $93.63   $93.65   $93.60  
  Purchase #4 $123.30   6.314%   $131.0852   $131.09   $131.10   $131.10  
  Purchase #5 $180.70   9.136%   $197.2088   $197.21   $197.20   $197.20  
  Purchase #6 $159.94   10.480%   $176.7017   $176.70   $176.70   $176.70  
  Purchase #7 $131.26   8.553%   $142.4867   $142.49   $142.50   $142.50  
  7 purchase totals = $925.39       $1,004.6883   $1,004.70   $1,004.70   $1,004.70