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 $63.47   11.763%   $70.936   $70.94   $70.95   $70.90  
  Purchase #2 $239.31   8.657%   $260.0271   $260.03   $260.05   $260.00  
  Purchase #3 $215.86   6.498%   $229.8866   $229.89   $229.90   $229.90  
  Purchase #4 $9.32   7.364%   $10.0063   $10.01   $10.00   $10.00  
  Purchase #5 $76.81   13.281%   $87.0111   $87.01   $87.00   $87.00  
  Purchase #6 $93.94   12.423%   $105.6102   $105.61   $105.60   $105.60  
  Purchase #7 $108.77   12.757%   $122.6458   $122.65   $122.65   $122.60  
  7 purchase totals = $807.48       $886.1231   $886.14   $886.15   $886.00