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 $72.71   4.504%   $75.9849   $75.98   $76.00   $76.00  
  Purchase #2 $66.32   5.488%   $69.9596   $69.96   $69.95   $70.00  
  Purchase #3 $158.80   8.202%   $171.8248   $171.82   $171.80   $171.80  
  Purchase #4 $76.27   13.675%   $86.6999   $86.70   $86.70   $86.70  
  Purchase #5 $141.62   5.597%   $149.5465   $149.55   $149.55   $149.50  
  Purchase #6 $155.64   13.798%   $177.1152   $177.12   $177.10   $177.10  
  Purchase #7 $31.91   8.156%   $34.5126   $34.51   $34.50   $34.50  
  7 purchase totals = $703.27       $765.6435   $765.64   $765.60   $765.60