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 $24.26   4.564%   $25.3672   $25.37   $25.35   $25.40  
  Purchase #2 $183.72   6.426%   $195.5258   $195.53   $195.55   $195.50  
  Purchase #3 $123.88   8.128%   $133.949   $133.95   $133.95   $133.90  
  Purchase #4 $14.80   11.813%   $16.5483   $16.55   $16.55   $16.50  
  Purchase #5 $185.97   8.739%   $202.2219   $202.22   $202.20   $202.20  
  Purchase #6 $53.53   9.777%   $58.7636   $58.76   $58.75   $58.80  
  Purchase #7 $123.54   13.850%   $140.6503   $140.65   $140.65   $140.70  
  7 purchase totals = $709.70       $773.0261   $773.03   $773.00   $773.00