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 $182.31   11.597%   $203.4525   $203.45   $203.45   $203.50  
  Purchase #2 $91.43   6.122%   $97.0273   $97.03   $97.05   $97.00  
  Purchase #3 $71.87   8.220%   $77.7777   $77.78   $77.80   $77.80  
  Purchase #4 $154.49   4.360%   $161.2258   $161.23   $161.25   $161.20  
  Purchase #5 $5.51   11.687%   $6.154   $6.15   $6.15   $6.20  
  Purchase #6 $102.97   13.402%   $116.77   $116.77   $116.75   $116.80  
  Purchase #7 $96.46   7.352%   $103.5517   $103.55   $103.55   $103.60  
  7 purchase totals = $705.04       $765.9590   $765.96   $766.00   $766.10