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 $23.73   6.173%   $25.1949   $25.19   $25.20   $25.20  
  Purchase #2 $246.38   4.291%   $256.9522   $256.95   $256.95   $257.00  
  Purchase #3 $195.80   5.185%   $205.9522   $205.95   $205.95   $206.00  
  Purchase #4 $47.85   3.739%   $49.6391   $49.64   $49.65   $49.60  
  Purchase #5 $237.45   10.366%   $262.0641   $262.06   $262.05   $262.10  
  Purchase #6 $29.73   5.785%   $31.4499   $31.45   $31.45   $31.40  
  Purchase #7 $85.30   10.531%   $94.2829   $94.28   $94.30   $94.30  
  7 purchase totals = $866.24       $925.5353   $925.52   $925.55   $925.60