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 $103.97   11.614%   $116.0451   $116.05   $116.05   $116.00  
  Purchase #2 $95.99   12.453%   $107.9436   $107.94   $107.95   $107.90  
  Purchase #3 $127.99   5.315%   $134.7927   $134.79   $134.80   $134.80  
  Purchase #4 $29.49   11.341%   $32.8345   $32.83   $32.85   $32.80  
  Purchase #5 $214.54   10.118%   $236.2472   $236.25   $236.25   $236.20  
  Purchase #6 $180.57   5.798%   $191.0394   $191.04   $191.05   $191.00  
  Purchase #7 $174.89   5.133%   $183.8671   $183.87   $183.85   $183.90  
  7 purchase totals = $927.44       $1,002.7696   $1,002.77   $1,002.80   $1,002.60