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 $73.94   3.715%   $76.6869   $76.69   $76.70   $76.70  
  Purchase #2 $112.61   8.728%   $122.4386   $122.44   $122.45   $122.40  
  Purchase #3 $171.36   5.540%   $180.8533   $180.85   $180.85   $180.90  
  Purchase #4 $200.42   10.505%   $221.4741   $221.47   $221.45   $221.50  
  Purchase #5 $77.95   11.442%   $86.869   $86.87   $86.85   $86.90  
  Purchase #6 $248.45   6.608%   $264.8676   $264.87   $264.85   $264.90  
  Purchase #7 $98.32   4.498%   $102.7424   $102.74   $102.75   $102.70  
  7 purchase totals = $983.05       $1,055.9319   $1,055.93   $1,055.90   $1,056.00