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 $241.86   10.598%   $267.4923   $267.49   $267.50   $267.50  
  Purchase #2 $35.25   13.192%   $39.9002   $39.90   $39.90   $39.90  
  Purchase #3 $247.28   9.646%   $271.1326   $271.13   $271.15   $271.10  
  Purchase #4 $208.43   8.135%   $225.3858   $225.39   $225.40   $225.40  
  Purchase #5 $215.77   11.818%   $241.2697   $241.27   $241.25   $241.30  
  Purchase #6 $244.98   13.503%   $278.0596   $278.06   $278.05   $278.10  
  Purchase #7 $172.48   5.373%   $181.7474   $181.75   $181.75   $181.70  
  7 purchase totals = $1,366.05       $1,504.9876   $1,504.99   $1,505.00   $1,505.00