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 $47.90   6.555%   $51.0398   $51.04   $51.05   $51.00  
  Purchase #2 $165.69   8.193%   $179.265   $179.27   $179.25   $179.30  
  Purchase #3 $57.91   12.849%   $65.3509   $65.35   $65.35   $65.40  
  Purchase #4 $165.96   10.870%   $183.9999   $184.00   $184.00   $184.00  
  Purchase #5 $117.35   6.259%   $124.6949   $124.69   $124.70   $124.70  
  Purchase #6 $39.69   4.795%   $41.5931   $41.59   $41.60   $41.60  
  Purchase #7 $68.71   10.466%   $75.9012   $75.90   $75.90   $75.90  
  7 purchase totals = $663.21       $721.8448   $721.84   $721.85   $721.90