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 $224.77   9.660%   $246.4828   $246.48   $246.50   $246.50  
  Purchase #2 $29.48   8.436%   $31.9669   $31.97   $31.95   $32.00  
  Purchase #3 $212.76   11.809%   $237.8848   $237.88   $237.90   $237.90  
  Purchase #4 $248.59   13.691%   $282.6245   $282.62   $282.60   $282.60  
  Purchase #5 $116.97   12.286%   $131.3409   $131.34   $131.35   $131.30  
  Purchase #6 $245.98   10.507%   $271.8251   $271.83   $271.85   $271.80  
  Purchase #7 $198.76   13.801%   $226.1909   $226.19   $226.20   $226.20  
  7 purchase totals = $1,277.31       $1,428.3159   $1,428.31   $1,428.35   $1,428.30