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 $68.34   13.629%   $77.6541   $77.65   $77.65   $77.70  
  Purchase #2 $14.30   12.386%   $16.0712   $16.07   $16.05   $16.10  
  Purchase #3 $172.47   5.794%   $182.4629   $182.46   $182.45   $182.50  
  Purchase #4 $151.61   10.153%   $167.003   $167.00   $167.00   $167.00  
  Purchase #5 $29.60   3.490%   $30.633   $30.63   $30.65   $30.60  
  Purchase #6 $109.98   13.381%   $124.6964   $124.70   $124.70   $124.70  
  Purchase #7 $85.59   11.713%   $95.6152   $95.62   $95.60   $95.60  
  7 purchase totals = $631.89       $694.1358   $694.13   $694.10   $694.20