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 $17.60   10.808%   $19.5022   $19.50   $19.50   $19.50  
  Purchase #2 $141.39   11.565%   $157.7418   $157.74   $157.75   $157.70  
  Purchase #3 $98.87   12.854%   $111.5787   $111.58   $111.60   $111.60  
  Purchase #4 $46.45   7.371%   $49.8738   $49.87   $49.85   $49.90  
  Purchase #5 $36.65   11.168%   $40.7431   $40.74   $40.75   $40.70  
  Purchase #6 $27.77   4.492%   $29.0174   $29.02   $29.00   $29.00  
  Purchase #7 $104.49   12.144%   $117.1793   $117.18   $117.20   $117.20  
  7 purchase totals = $473.22       $525.6363   $525.63   $525.65   $525.60