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 $108.31   7.262%   $116.1755   $116.18   $116.20   $116.20  
  Purchase #2 $169.47   12.271%   $190.2657   $190.27   $190.25   $190.30  
  Purchase #3 $26.76   8.838%   $29.125   $29.13   $29.15   $29.10  
  Purchase #4 $79.91   9.623%   $87.5997   $87.60   $87.60   $87.60  
  Purchase #5 $93.98   4.491%   $98.2006   $98.20   $98.20   $98.20  
  Purchase #6 $201.51   11.819%   $225.3265   $225.33   $225.35   $225.30  
  Purchase #7 $183.67   12.722%   $207.0365   $207.04   $207.05   $207.00  
  7 purchase totals = $863.61       $953.7295   $953.75   $953.80   $953.70