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 $64.44   12.605%   $72.5627   $72.56   $72.55   $72.60  
  Purchase #2 $186.80   11.147%   $207.6226   $207.62   $207.60   $207.60  
  Purchase #3 $36.66   13.726%   $41.692   $41.69   $41.70   $41.70  
  Purchase #4 $27.87   8.386%   $30.2072   $30.21   $30.20   $30.20  
  Purchase #5 $239.46   3.366%   $247.5202   $247.52   $247.50   $247.50  
  Purchase #6 $245.66   13.650%   $279.1926   $279.19   $279.20   $279.20  
  Purchase #7 $148.81   10.195%   $163.9812   $163.98   $164.00   $164.00  
  7 purchase totals = $949.70       $1,042.7785   $1,042.77   $1,042.75   $1,042.80