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 $14.46   4.862%   $15.163   $15.16   $15.15   $15.20  
  Purchase #2 $62.55   13.112%   $70.7516   $70.75   $70.75   $70.80  
  Purchase #3 $83.61   9.162%   $91.2703   $91.27   $91.25   $91.30  
  Purchase #4 $242.49   4.182%   $252.6309   $252.63   $252.65   $252.60  
  Purchase #5 $225.33   12.855%   $254.2962   $254.30   $254.30   $254.30  
  Purchase #6 $97.42   6.847%   $104.0903   $104.09   $104.10   $104.10  
  Purchase #7 $190.94   12.456%   $214.7235   $214.72   $214.70   $214.70  
  7 purchase totals = $916.80       $1,002.9258   $1,002.92   $1,002.90   $1,003.00