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 $86.84   8.260%   $94.013   $94.01   $94.00   $94.00  
  Purchase #2 $119.80   12.777%   $135.1068   $135.11   $135.10   $135.10  
  Purchase #3 $227.70   13.102%   $257.5333   $257.53   $257.55   $257.50  
  Purchase #4 $11.67   6.296%   $12.4047   $12.40   $12.40   $12.40  
  Purchase #5 $42.54   7.228%   $45.6148   $45.61   $45.60   $45.60  
  Purchase #6 $232.63   5.498%   $245.42   $245.42   $245.40   $245.40  
  Purchase #7 $26.28   11.270%   $29.2418   $29.24   $29.25   $29.20  
  7 purchase totals = $747.46       $819.3344   $819.32   $819.30   $819.20