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 $114.56   10.672%   $126.7858   $126.79   $126.80   $126.80  
  Purchase #2 $28.92   3.397%   $29.9024   $29.90   $29.90   $29.90  
  Purchase #3 $70.27   13.559%   $79.7979   $79.80   $79.80   $79.80  
  Purchase #4 $249.92   6.799%   $266.9121   $266.91   $266.90   $266.90  
  Purchase #5 $68.27   11.710%   $76.2644   $76.26   $76.25   $76.30  
  Purchase #6 $44.55   7.717%   $47.9879   $47.99   $48.00   $48.00  
  Purchase #7 $220.27   10.302%   $242.9622   $242.96   $242.95   $243.00  
  7 purchase totals = $796.76       $870.6127   $870.61   $870.60   $870.70