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 $53.73   11.602%   $59.9638   $59.96   $59.95   $60.00  
  Purchase #2 $210.99   9.786%   $231.6375   $231.64   $231.65   $231.60  
  Purchase #3 $39.93   11.709%   $44.6054   $44.61   $44.60   $44.60  
  Purchase #4 $16.99   7.557%   $18.2739   $18.27   $18.25   $18.30  
  Purchase #5 $113.58   6.257%   $120.6867   $120.69   $120.70   $120.70  
  Purchase #6 $69.62   13.814%   $79.2373   $79.24   $79.25   $79.20  
  Purchase #7 $72.94   4.505%   $76.2259   $76.23   $76.25   $76.20  
  7 purchase totals = $577.78       $630.6305   $630.64   $630.65   $630.60