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 $61.27   11.510%   $68.3222   $68.32   $68.30   $68.30  
  Purchase #2 $56.88   10.487%   $62.845   $62.85   $62.85   $62.80  
  Purchase #3 $210.61   7.303%   $225.9908   $225.99   $226.00   $226.00  
  Purchase #4 $13.53   8.629%   $14.6975   $14.70   $14.70   $14.70  
  Purchase #5 $50.76   13.370%   $57.5466   $57.55   $57.55   $57.50  
  Purchase #6 $248.61   3.331%   $256.8912   $256.89   $256.90   $256.90  
  Purchase #7 $70.88   3.114%   $73.0872   $73.09   $73.10   $73.10  
  7 purchase totals = $712.54       $759.3805   $759.39   $759.40   $759.30