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 $33.63   11.674%   $37.556   $37.56   $37.55   $37.60  
  Purchase #2 $208.67   7.327%   $223.9593   $223.96   $223.95   $224.00  
  Purchase #3 $81.37   9.179%   $88.839   $88.84   $88.85   $88.80  
  Purchase #4 $150.38   6.226%   $159.7427   $159.74   $159.75   $159.70  
  Purchase #5 $104.71   5.589%   $110.5622   $110.56   $110.55   $110.60  
  Purchase #6 $227.98   5.542%   $240.6147   $240.61   $240.60   $240.60  
  Purchase #7 $53.34   8.411%   $57.8264   $57.83   $57.85   $57.80  
  7 purchase totals = $860.08       $919.1003   $919.10   $919.10   $919.10