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 $193.55   10.261%   $213.4102   $213.41   $213.40   $213.40  
  Purchase #2 $244.33   13.354%   $276.9578   $276.96   $276.95   $277.00  
  Purchase #3 $40.61   3.167%   $41.8961   $41.90   $41.90   $41.90  
  Purchase #4 $218.76   4.438%   $228.4686   $228.47   $228.45   $228.50  
  Purchase #5 $16.43   12.437%   $18.4734   $18.47   $18.45   $18.50  
  Purchase #6 $249.25   9.120%   $271.9816   $271.98   $272.00   $272.00  
  Purchase #7 $185.65   13.177%   $210.1131   $210.11   $210.10   $210.10  
  7 purchase totals = $1,148.58       $1,261.3008   $1,261.30   $1,261.25   $1,261.40