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 $194.91   7.411%   $209.3548   $209.35   $209.35   $209.40  
  Purchase #2 $204.96   13.169%   $231.9512   $231.95   $231.95   $232.00  
  Purchase #3 $62.88   4.694%   $65.8316   $65.83   $65.85   $65.80  
  Purchase #4 $46.58   13.796%   $53.0062   $53.01   $53.00   $53.00  
  Purchase #5 $103.47   9.501%   $113.3007   $113.30   $113.30   $113.30  
  Purchase #6 $199.88   7.109%   $214.0895   $214.09   $214.10   $214.10  
  Purchase #7 $42.50   9.307%   $46.4555   $46.46   $46.45   $46.50  
  7 purchase totals = $855.18       $933.9895   $933.99   $934.00   $934.10