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 $186.94   13.265%   $211.7376   $211.74   $211.75   $211.70  
  Purchase #2 $240.90   10.384%   $265.9151   $265.92   $265.90   $265.90  
  Purchase #3 $115.89   7.435%   $124.5064   $124.51   $124.50   $124.50  
  Purchase #4 $23.79   3.750%   $24.6821   $24.68   $24.70   $24.70  
  Purchase #5 $136.84   7.793%   $147.5039   $147.50   $147.50   $147.50  
  Purchase #6 $32.91   9.834%   $36.1464   $36.15   $36.15   $36.10  
  Purchase #7 $195.59   5.259%   $205.8761   $205.88   $205.90   $205.90  
  7 purchase totals = $932.86       $1,016.3676   $1,016.38   $1,016.40   $1,016.30