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 $64.49   5.448%   $68.0034   $68.00   $68.00   $68.00  
  Purchase #2 $149.43   4.408%   $156.0169   $156.02   $156.00   $156.00  
  Purchase #3 $49.66   13.408%   $56.3184   $56.32   $56.30   $56.30  
  Purchase #4 $122.56   11.536%   $136.6985   $136.70   $136.70   $136.70  
  Purchase #5 $195.65   13.171%   $221.4191   $221.42   $221.40   $221.40  
  Purchase #6 $116.85   3.118%   $120.4934   $120.49   $120.50   $120.50  
  Purchase #7 $120.41   4.796%   $126.1849   $126.18   $126.20   $126.20  
  7 purchase totals = $819.05       $885.1346   $885.13   $885.10   $885.10