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 $223.31   13.760%   $254.0375   $254.04   $254.05   $254.00  
  Purchase #2 $17.94   8.292%   $19.4276   $19.43   $19.45   $19.40  
  Purchase #3 $216.75   11.249%   $241.1322   $241.13   $241.15   $241.10  
  Purchase #4 $70.85   8.263%   $76.7043   $76.70   $76.70   $76.70  
  Purchase #5 $13.91   4.319%   $14.5108   $14.51   $14.50   $14.50  
  Purchase #6 $231.74   4.606%   $242.4139   $242.41   $242.40   $242.40  
  Purchase #7 $160.83   9.118%   $175.4945   $175.49   $175.50   $175.50  
  7 purchase totals = $935.33       $1,023.7208   $1,023.71   $1,023.75   $1,023.60