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 $74.59   12.375%   $83.8205   $83.82   $83.80   $83.80  
  Purchase #2 $168.67   7.281%   $180.9509   $180.95   $180.95   $181.00  
  Purchase #3 $106.99   8.569%   $116.158   $116.16   $116.15   $116.20  
  Purchase #4 $62.46   5.854%   $66.1164   $66.12   $66.10   $66.10  
  Purchase #5 $77.83   11.396%   $86.6995   $86.70   $86.70   $86.70  
  Purchase #6 $120.49   7.465%   $129.4846   $129.48   $129.50   $129.50  
  Purchase #7 $238.95   5.855%   $252.9405   $252.94   $252.95   $252.90  
  7 purchase totals = $849.98       $916.1704   $916.17   $916.15   $916.20