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 $31.61   7.402%   $33.9498   $33.95   $33.95   $33.90  
  Purchase #2 $235.32   3.708%   $244.0457   $244.05   $244.05   $244.00  
  Purchase #3 $214.66   5.237%   $225.9017   $225.90   $225.90   $225.90  
  Purchase #4 $173.27   8.357%   $187.7502   $187.75   $187.75   $187.80  
  Purchase #5 $198.94   13.151%   $225.1026   $225.10   $225.10   $225.10  
  Purchase #6 $247.78   11.198%   $275.5264   $275.53   $275.55   $275.50  
  Purchase #7 $199.36   13.823%   $226.9175   $226.92   $226.90   $226.90  
  7 purchase totals = $1,300.94       $1,419.1939   $1,419.20   $1,419.20   $1,419.10