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 $197.98   13.213%   $224.1391   $224.14   $224.15   $224.10  
  Purchase #2 $156.97   3.607%   $162.6319   $162.63   $162.65   $162.60  
  Purchase #3 $249.48   5.514%   $263.2363   $263.24   $263.25   $263.20  
  Purchase #4 $92.49   12.391%   $103.9504   $103.95   $103.95   $104.00  
  Purchase #5 $185.52   13.550%   $210.658   $210.66   $210.65   $210.70  
  Purchase #6 $194.84   11.702%   $217.6402   $217.64   $217.65   $217.60  
  Purchase #7 $177.60   10.307%   $195.9052   $195.91   $195.90   $195.90  
  7 purchase totals = $1,254.88       $1,378.1611   $1,378.17   $1,378.20   $1,378.10