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 $14.54   9.484%   $15.919   $15.92   $15.90   $15.90  
  Purchase #2 $223.42   7.227%   $239.5666   $239.57   $239.55   $239.60  
  Purchase #3 $242.97   8.739%   $264.2031   $264.20   $264.20   $264.20  
  Purchase #4 $109.50   7.373%   $117.5734   $117.57   $117.55   $117.60  
  Purchase #5 $225.87   4.467%   $235.9596   $235.96   $235.95   $236.00  
  Purchase #6 $191.72   9.247%   $209.4483   $209.45   $209.45   $209.40  
  Purchase #7 $106.71   8.111%   $115.3652   $115.37   $115.35   $115.40  
  7 purchase totals = $1,114.73       $1,198.0352   $1,198.04   $1,197.95   $1,198.10