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 $61.86   3.388%   $63.9558   $63.96   $63.95   $64.00  
  Purchase #2 $41.30   11.580%   $46.0825   $46.08   $46.10   $46.10  
  Purchase #3 $69.99   10.379%   $77.2543   $77.25   $77.25   $77.30  
  Purchase #4 $93.62   4.137%   $97.4931   $97.49   $97.50   $97.50  
  Purchase #5 $57.83   5.450%   $60.9817   $60.98   $61.00   $61.00  
  Purchase #6 $88.56   12.197%   $99.3617   $99.36   $99.35   $99.40  
  Purchase #7 $106.67   3.315%   $110.2061   $110.21   $110.20   $110.20  
  7 purchase totals = $519.83       $555.3352   $555.33   $555.35   $555.50