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 $86.91   8.559%   $94.3486   $94.35   $94.35   $94.30  
  Purchase #2 $201.31   6.787%   $214.9729   $214.97   $214.95   $215.00  
  Purchase #3 $102.95   11.315%   $114.5988   $114.60   $114.60   $114.60  
  Purchase #4 $196.41   6.228%   $208.6424   $208.64   $208.65   $208.60  
  Purchase #5 $235.89   8.437%   $255.792   $255.79   $255.80   $255.80  
  Purchase #6 $25.67   13.112%   $29.0359   $29.04   $29.05   $29.00  
  Purchase #7 $16.32   4.123%   $16.9929   $16.99   $17.00   $17.00  
  7 purchase totals = $865.46       $934.3835   $934.38   $934.40   $934.30