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 $116.97   8.457%   $126.8622   $126.86   $126.85   $126.90  
  Purchase #2 $53.57   13.568%   $60.8384   $60.84   $60.85   $60.80  
  Purchase #3 $57.99   5.532%   $61.198   $61.20   $61.20   $61.20  
  Purchase #4 $52.84   7.147%   $56.6165   $56.62   $56.60   $56.60  
  Purchase #5 $217.80   7.399%   $233.915   $233.92   $233.90   $233.90  
  Purchase #6 $55.81   10.298%   $61.5573   $61.56   $61.55   $61.60  
  Purchase #7 $178.58   6.539%   $190.2573   $190.26   $190.25   $190.30  
  7 purchase totals = $733.56       $791.2447   $791.26   $791.20   $791.30