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 $116.47   11.448%   $129.8035   $129.80   $129.80   $129.80  
  Purchase #2 $62.70   13.105%   $70.9168   $70.92   $70.90   $70.90  
  Purchase #3 $151.49   4.665%   $158.557   $158.56   $158.55   $158.60  
  Purchase #4 $209.93   13.609%   $238.4994   $238.50   $238.50   $238.50  
  Purchase #5 $231.28   11.186%   $257.151   $257.15   $257.15   $257.20  
  Purchase #6 $73.55   9.408%   $80.4696   $80.47   $80.45   $80.50  
  Purchase #7 $213.29   8.775%   $232.0062   $232.01   $232.00   $232.00  
  7 purchase totals = $1,058.71       $1,167.4035   $1,167.41   $1,167.35   $1,167.50