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 $22.76   7.331%   $24.4285   $24.43   $24.45   $24.40  
  Purchase #2 $193.34   13.463%   $219.3694   $219.37   $219.35   $219.40  
  Purchase #3 $236.59   8.778%   $257.3579   $257.36   $257.35   $257.40  
  Purchase #4 $212.75   7.190%   $228.0467   $228.05   $228.05   $228.00  
  Purchase #5 $205.75   11.636%   $229.6911   $229.69   $229.70   $229.70  
  Purchase #6 $181.75   9.314%   $198.6782   $198.68   $198.70   $198.70  
  Purchase #7 $129.39   10.552%   $143.0432   $143.04   $143.05   $143.00  
  7 purchase totals = $1,182.33       $1,300.6150   $1,300.62   $1,300.65   $1,300.60