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 $81.69   3.146%   $84.26   $84.26   $84.25   $84.30  
  Purchase #2 $213.69   3.526%   $221.2247   $221.22   $221.20   $221.20  
  Purchase #3 $195.71   10.802%   $216.8506   $216.85   $216.85   $216.90  
  Purchase #4 $62.73   4.248%   $65.3948   $65.39   $65.40   $65.40  
  Purchase #5 $63.44   9.836%   $69.68   $69.68   $69.70   $69.70  
  Purchase #6 $95.77   8.364%   $103.7802   $103.78   $103.80   $103.80  
  Purchase #7 $224.32   13.643%   $254.924   $254.92   $254.90   $254.90  
  7 purchase totals = $937.35       $1,016.1143   $1,016.10   $1,016.10   $1,016.20