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 $12.26   3.648%   $12.7072   $12.71   $12.70   $12.70  
  Purchase #2 $83.71   8.773%   $91.0539   $91.05   $91.05   $91.10  
  Purchase #3 $80.99   6.533%   $86.2811   $86.28   $86.30   $86.30  
  Purchase #4 $97.27   3.501%   $100.6754   $100.68   $100.70   $100.70  
  Purchase #5 $96.92   11.495%   $108.061   $108.06   $108.05   $108.10  
  Purchase #6 $98.35   11.523%   $109.6829   $109.68   $109.70   $109.70  
  Purchase #7 $129.32   12.707%   $145.7527   $145.75   $145.75   $145.80  
  7 purchase totals = $598.82       $654.2142   $654.21   $654.25   $654.40