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 $67.63   5.723%   $71.5005   $71.50   $71.50   $71.50  
  Purchase #2 $213.66   13.519%   $242.5447   $242.54   $242.55   $242.50  
  Purchase #3 $70.83   12.744%   $79.8566   $79.86   $79.85   $79.90  
  Purchase #4 $22.79   4.761%   $23.875   $23.88   $23.90   $23.90  
  Purchase #5 $189.94   6.721%   $202.7059   $202.71   $202.70   $202.70  
  Purchase #6 $92.96   13.276%   $105.3014   $105.30   $105.30   $105.30  
  Purchase #7 $170.99   5.405%   $180.232   $180.23   $180.25   $180.20  
  7 purchase totals = $828.80       $906.0161   $906.02   $906.05   $906.00