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 $216.77   11.602%   $241.9197   $241.92   $241.90   $241.90  
  Purchase #2 $202.65   3.394%   $209.5279   $209.53   $209.55   $209.50  
  Purchase #3 $161.77   4.461%   $168.9866   $168.99   $169.00   $169.00  
  Purchase #4 $244.95   11.146%   $272.2521   $272.25   $272.25   $272.30  
  Purchase #5 $193.35   7.268%   $207.4027   $207.40   $207.40   $207.40  
  Purchase #6 $90.83   12.212%   $101.9222   $101.92   $101.90   $101.90  
  Purchase #7 $210.39   3.688%   $218.1492   $218.15   $218.15   $218.10  
  7 purchase totals = $1,320.71       $1,420.1604   $1,420.16   $1,420.15   $1,420.10