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 $203.41   6.214%   $216.0499   $216.05   $216.05   $216.00  
  Purchase #2 $25.77   9.295%   $28.1653   $28.17   $28.15   $28.20  
  Purchase #3 $202.59   5.711%   $214.1599   $214.16   $214.15   $214.20  
  Purchase #4 $70.39   4.820%   $73.7828   $73.78   $73.80   $73.80  
  Purchase #5 $105.74   6.203%   $112.2991   $112.30   $112.30   $112.30  
  Purchase #6 $77.43   8.744%   $84.2005   $84.20   $84.20   $84.20  
  Purchase #7 $32.95   6.222%   $35.0001   $35.00   $35.00   $35.00  
  7 purchase totals = $718.28       $763.6576   $763.66   $763.65   $763.70