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 $64.51   13.865%   $73.4543   $73.45   $73.45   $73.50  
  Purchase #2 $209.78   9.748%   $230.2294   $230.23   $230.25   $230.20  
  Purchase #3 $105.66   9.652%   $115.8583   $115.86   $115.85   $115.90  
  Purchase #4 $164.42   3.371%   $169.9626   $169.96   $169.95   $170.00  
  Purchase #5 $197.68   10.621%   $218.6756   $218.68   $218.70   $218.70  
  Purchase #6 $131.74   7.286%   $141.3386   $141.34   $141.35   $141.30  
  Purchase #7 $106.65   6.103%   $113.1588   $113.16   $113.15   $113.20  
  7 purchase totals = $980.44       $1,062.6776   $1,062.68   $1,062.70   $1,062.80