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 $86.89   9.692%   $95.3114   $95.31   $95.30   $95.30  
  Purchase #2 $57.99   4.790%   $60.7677   $60.77   $60.75   $60.80  
  Purchase #3 $108.86   3.827%   $113.0261   $113.03   $113.05   $113.00  
  Purchase #4 $141.28   6.299%   $150.1792   $150.18   $150.20   $150.20  
  Purchase #5 $206.28   7.564%   $221.883   $221.88   $221.90   $221.90  
  Purchase #6 $119.71   11.115%   $133.0158   $133.02   $133.00   $133.00  
  Purchase #7 $77.51   6.802%   $82.7822   $82.78   $82.80   $82.80  
  7 purchase totals = $798.52       $856.9654   $856.97   $857.00   $857.00