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 $148.46   6.710%   $158.4217   $158.42   $158.40   $158.40  
  Purchase #2 $14.82   11.820%   $16.5717   $16.57   $16.55   $16.60  
  Purchase #3 $118.73   7.773%   $127.9589   $127.96   $127.95   $128.00  
  Purchase #4 $95.44   6.361%   $101.5109   $101.51   $101.50   $101.50  
  Purchase #5 $194.30   3.824%   $201.73   $201.73   $201.75   $201.70  
  Purchase #6 $76.48   6.535%   $81.478   $81.48   $81.50   $81.50  
  Purchase #7 $44.25   7.344%   $47.4997   $47.50   $47.50   $47.50  
  7 purchase totals = $692.48       $735.1709   $735.17   $735.15   $735.20