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 $246.75   7.808%   $266.0162   $266.02   $266.00   $266.00  
  Purchase #2 $24.30   4.632%   $25.4256   $25.43   $25.45   $25.40  
  Purchase #3 $123.28   7.659%   $132.722   $132.72   $132.70   $132.70  
  Purchase #4 $44.29   6.535%   $47.1844   $47.18   $47.20   $47.20  
  Purchase #5 $63.63   7.495%   $68.3991   $68.40   $68.40   $68.40  
  Purchase #6 $236.91   7.305%   $254.2163   $254.22   $254.20   $254.20  
  Purchase #7 $68.25   7.869%   $73.6206   $73.62   $73.60   $73.60  
  7 purchase totals = $807.41       $867.5842   $867.59   $867.55   $867.50