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 $23.49   5.806%   $24.8538   $24.85   $24.85   $24.90  
  Purchase #2 $184.25   5.855%   $195.0378   $195.04   $195.05   $195.00  
  Purchase #3 $79.89   5.469%   $84.2592   $84.26   $84.25   $84.30  
  Purchase #4 $56.36   3.223%   $58.1765   $58.18   $58.20   $58.20  
  Purchase #5 $141.27   6.275%   $150.1347   $150.13   $150.15   $150.10  
  Purchase #6 $64.49   5.291%   $67.9022   $67.90   $67.90   $67.90  
  Purchase #7 $70.77   8.198%   $76.5717   $76.57   $76.55   $76.60  
  7 purchase totals = $620.52       $656.9359   $656.93   $656.95   $657.00