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 $23.36   11.297%   $25.999   $26.00   $26.00   $26.00  
  Purchase #2 $68.45   4.418%   $71.4741   $71.47   $71.45   $71.50  
  Purchase #3 $100.69   13.218%   $113.9992   $114.00   $114.00   $114.00  
  Purchase #4 $125.93   9.486%   $137.8757   $137.88   $137.90   $137.90  
  Purchase #5 $186.55   8.182%   $201.8135   $201.81   $201.80   $201.80  
  Purchase #6 $43.39   6.135%   $46.052   $46.05   $46.05   $46.10  
  Purchase #7 $156.88   8.370%   $170.0109   $170.01   $170.00   $170.00  
  7 purchase totals = $705.25       $767.2244   $767.22   $767.20   $767.30