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 $58.47   6.467%   $62.2513   $62.25   $62.25   $62.30  
  Purchase #2 $67.78   8.802%   $73.746   $73.75   $73.75   $73.70  
  Purchase #3 $10.54   6.138%   $11.1869   $11.19   $11.20   $11.20  
  Purchase #4 $64.49   7.778%   $69.506   $69.51   $69.50   $69.50  
  Purchase #5 $247.73   13.102%   $280.1876   $280.19   $280.20   $280.20  
  Purchase #6 $54.70   5.254%   $57.5739   $57.57   $57.55   $57.60  
  Purchase #7 $225.28   7.441%   $242.0431   $242.04   $242.05   $242.00  
  7 purchase totals = $728.99       $796.4948   $796.50   $796.50   $796.50