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 $201.39   8.616%   $218.7418   $218.74   $218.75   $218.70  
  Purchase #2 $234.85   13.689%   $266.9986   $267.00   $267.00   $267.00  
  Purchase #3 $234.97   9.848%   $258.1098   $258.11   $258.10   $258.10  
  Purchase #4 $168.47   11.874%   $188.4741   $188.47   $188.45   $188.50  
  Purchase #5 $107.64   4.109%   $112.0629   $112.06   $112.05   $112.10  
  Purchase #6 $120.37   6.599%   $128.3132   $128.31   $128.30   $128.30  
  Purchase #7 $205.53   8.211%   $222.4061   $222.41   $222.40   $222.40  
  7 purchase totals = $1,273.22       $1,395.1065   $1,395.10   $1,395.05   $1,395.10