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   12.708%   $26.3286   $26.33   $26.35   $26.30  
  Purchase #2 $232.62   11.222%   $258.7246   $258.72   $258.70   $258.70  
  Purchase #3 $116.32   9.538%   $127.4146   $127.41   $127.40   $127.40  
  Purchase #4 $201.92   12.532%   $227.2246   $227.22   $227.20   $227.20  
  Purchase #5 $37.58   5.615%   $39.6901   $39.69   $39.70   $39.70  
  Purchase #6 $55.55   13.709%   $63.1653   $63.17   $63.15   $63.20  
  Purchase #7 $9.58   7.260%   $10.2755   $10.28   $10.30   $10.30  
  7 purchase totals = $676.93       $752.8233   $752.82   $752.80   $752.80