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 $30.69   9.161%   $33.5015   $33.50   $33.50   $33.50  
  Purchase #2 $112.64   4.255%   $117.4328   $117.43   $117.45   $117.40  
  Purchase #3 $149.59   13.160%   $169.276   $169.28   $169.30   $169.30  
  Purchase #4 $144.74   6.480%   $154.1192   $154.12   $154.10   $154.10  
  Purchase #5 $193.63   5.756%   $204.7753   $204.78   $204.80   $204.80  
  Purchase #6 $134.32   12.688%   $151.3625   $151.36   $151.35   $151.40  
  Purchase #7 $168.82   7.272%   $181.0966   $181.10   $181.10   $181.10  
  7 purchase totals = $934.43       $1,011.5639   $1,011.57   $1,011.60   $1,011.60