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 $73.29   3.104%   $75.5649   $75.56   $75.55   $75.60  
  Purchase #2 $201.51   6.633%   $214.8762   $214.88   $214.90   $214.90  
  Purchase #3 $21.30   8.152%   $23.0364   $23.04   $23.05   $23.00  
  Purchase #4 $190.97   10.544%   $211.1059   $211.11   $211.10   $211.10  
  Purchase #5 $137.34   3.602%   $142.287   $142.29   $142.30   $142.30  
  Purchase #6 $118.41   12.754%   $133.512   $133.51   $133.50   $133.50  
  Purchase #7 $53.77   6.367%   $57.1935   $57.19   $57.20   $57.20  
  7 purchase totals = $796.59       $857.5759   $857.58   $857.60   $857.60