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 $203.33   13.220%   $230.2102   $230.21   $230.20   $230.20  
  Purchase #2 $162.39   4.258%   $169.3046   $169.30   $169.30   $169.30  
  Purchase #3 $183.78   10.256%   $202.6285   $202.63   $202.65   $202.60  
  Purchase #4 $248.69   5.155%   $261.51   $261.51   $261.50   $261.50  
  Purchase #5 $39.62   10.390%   $43.7365   $43.74   $43.75   $43.70  
  Purchase #6 $249.29   5.332%   $262.5821   $262.58   $262.60   $262.60  
  Purchase #7 $68.73   13.405%   $77.9433   $77.94   $77.95   $77.90  
  7 purchase totals = $1,155.83       $1,247.9152   $1,247.91   $1,247.95   $1,247.80