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 $241.99   4.157%   $252.0495   $252.05   $252.05   $252.00  
  Purchase #2 $248.32   7.526%   $267.0086   $267.01   $267.00   $267.00  
  Purchase #3 $56.77   8.764%   $61.7453   $61.75   $61.75   $61.70  
  Purchase #4 $195.74   11.664%   $218.5711   $218.57   $218.55   $218.60  
  Purchase #5 $198.73   7.139%   $212.9173   $212.92   $212.90   $212.90  
  Purchase #6 $86.94   8.684%   $94.4899   $94.49   $94.50   $94.50  
  Purchase #7 $50.36   6.712%   $53.7402   $53.74   $53.75   $53.70  
  7 purchase totals = $1,078.85       $1,160.5219   $1,160.53   $1,160.50   $1,160.40