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 $182.86   11.571%   $204.0187   $204.02   $204.00   $204.00  
  Purchase #2 $233.75   8.342%   $253.2494   $253.25   $253.25   $253.20  
  Purchase #3 $142.80   10.713%   $158.0982   $158.10   $158.10   $158.10  
  Purchase #4 $220.35   10.665%   $243.8503   $243.85   $243.85   $243.90  
  Purchase #5 $57.88   12.474%   $65.1   $65.10   $65.10   $65.10  
  Purchase #6 $151.29   5.209%   $159.1707   $159.17   $159.15   $159.20  
  Purchase #7 $154.72   6.480%   $164.7459   $164.75   $164.75   $164.70  
  7 purchase totals = $1,143.65       $1,248.2332   $1,248.24   $1,248.20   $1,248.20