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 $182.62   13.420%   $207.1276   $207.13   $207.15   $207.10  
  Purchase #2 $21.68   10.495%   $23.9553   $23.96   $23.95   $24.00  
  Purchase #3 $41.67   6.762%   $44.4877   $44.49   $44.50   $44.50  
  Purchase #4 $185.75   11.623%   $207.3397   $207.34   $207.35   $207.30  
  Purchase #5 $188.27   11.734%   $210.3616   $210.36   $210.35   $210.40  
  Purchase #6 $206.29   12.605%   $232.2929   $232.29   $232.30   $232.30  
  Purchase #7 $250.75   7.872%   $270.489   $270.49   $270.50   $270.50  
  7 purchase totals = $1,077.03       $1,196.0538   $1,196.06   $1,196.10   $1,196.10