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 $250.83   6.806%   $267.9015   $267.90   $267.90   $267.90  
  Purchase #2 $115.74   5.842%   $122.5015   $122.50   $122.50   $122.50  
  Purchase #3 $76.54   6.471%   $81.4929   $81.49   $81.50   $81.50  
  Purchase #4 $58.40   10.177%   $64.3434   $64.34   $64.35   $64.30  
  Purchase #5 $62.44   4.830%   $65.4559   $65.46   $65.45   $65.50  
  Purchase #6 $36.94   11.250%   $41.0958   $41.10   $41.10   $41.10  
  Purchase #7 $101.87   6.705%   $108.7004   $108.70   $108.70   $108.70  
  7 purchase totals = $702.76       $751.4914   $751.49   $751.50   $751.50