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 $116.82   3.235%   $120.5991   $120.60   $120.60   $120.60  
  Purchase #2 $50.75   11.341%   $56.5056   $56.51   $56.50   $56.50  
  Purchase #3 $74.25   4.407%   $77.5222   $77.52   $77.50   $77.50  
  Purchase #4 $57.94   13.476%   $65.748   $65.75   $65.75   $65.70  
  Purchase #5 $201.47   4.491%   $210.518   $210.52   $210.50   $210.50  
  Purchase #6 $56.31   13.838%   $64.1022   $64.10   $64.10   $64.10  
  Purchase #7 $193.55   10.672%   $214.2057   $214.21   $214.20   $214.20  
  7 purchase totals = $751.09       $809.2008   $809.21   $809.15   $809.10