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 $95.53   11.508%   $106.5236   $106.52   $106.50   $106.50  
  Purchase #2 $23.71   12.721%   $26.7261   $26.73   $26.75   $26.70  
  Purchase #3 $214.93   7.166%   $230.3319   $230.33   $230.35   $230.30  
  Purchase #4 $53.49   12.358%   $60.1003   $60.10   $60.10   $60.10  
  Purchase #5 $169.41   13.247%   $191.8517   $191.85   $191.85   $191.90  
  Purchase #6 $198.58   5.735%   $209.9686   $209.97   $209.95   $210.00  
  Purchase #7 $137.72   3.308%   $142.2758   $142.28   $142.30   $142.30  
  7 purchase totals = $893.37       $967.7780   $967.78   $967.80   $967.80