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 $185.93   11.523%   $207.3547   $207.35   $207.35   $207.40  
  Purchase #2 $109.49   7.341%   $117.5277   $117.53   $117.55   $117.50  
  Purchase #3 $53.25   5.225%   $56.0323   $56.03   $56.05   $56.00  
  Purchase #4 $5.49   11.701%   $6.1324   $6.13   $6.15   $6.10  
  Purchase #5 $230.60   8.160%   $249.417   $249.42   $249.40   $249.40  
  Purchase #6 $55.94   11.121%   $62.1611   $62.16   $62.15   $62.20  
  Purchase #7 $24.71   5.279%   $26.0144   $26.01   $26.00   $26.00  
  7 purchase totals = $665.41       $724.6396   $724.63   $724.65   $724.60