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 $18.79   8.699%   $20.4245   $20.42   $20.40   $20.40  
  Purchase #2 $197.48   6.547%   $210.409   $210.41   $210.40   $210.40  
  Purchase #3 $36.65   9.472%   $40.1215   $40.12   $40.10   $40.10  
  Purchase #4 $145.72   3.126%   $150.2752   $150.28   $150.30   $150.30  
  Purchase #5 $218.26   8.719%   $237.2901   $237.29   $237.30   $237.30  
  Purchase #6 $225.83   6.385%   $240.2492   $240.25   $240.25   $240.20  
  Purchase #7 $193.49   7.435%   $207.876   $207.88   $207.90   $207.90  
  7 purchase totals = $1,036.22       $1,106.6455   $1,106.65   $1,106.65   $1,106.60