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 $59.74   12.835%   $67.4076   $67.41   $67.40   $67.40  
  Purchase #2 $202.62   5.698%   $214.1653   $214.17   $214.15   $214.20  
  Purchase #3 $29.77   11.327%   $33.142   $33.14   $33.15   $33.10  
  Purchase #4 $244.79   7.766%   $263.8004   $263.80   $263.80   $263.80  
  Purchase #5 $16.80   7.722%   $18.0973   $18.10   $18.10   $18.10  
  Purchase #6 $62.75   13.159%   $71.0073   $71.01   $71.00   $71.00  
  Purchase #7 $206.55   6.863%   $220.7255   $220.73   $220.75   $220.70  
  7 purchase totals = $823.02       $888.3454   $888.36   $888.35   $888.30