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 $182.67   10.742%   $202.2924   $202.29   $202.30   $202.30  
  Purchase #2 $96.86   6.262%   $102.9254   $102.93   $102.95   $102.90  
  Purchase #3 $25.65   10.780%   $28.4151   $28.42   $28.40   $28.40  
  Purchase #4 $78.58   6.716%   $83.8574   $83.86   $83.85   $83.90  
  Purchase #5 $15.44   7.590%   $16.6119   $16.61   $16.60   $16.60  
  Purchase #6 $244.79   13.469%   $277.7608   $277.76   $277.75   $277.80  
  Purchase #7 $37.80   7.244%   $40.5382   $40.54   $40.55   $40.50  
  7 purchase totals = $681.79       $752.4012   $752.41   $752.40   $752.40