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 $23.64   12.155%   $26.5134   $26.51   $26.50   $26.50  
  Purchase #2 $125.68   13.138%   $142.1918   $142.19   $142.20   $142.20  
  Purchase #3 $141.49   12.397%   $159.0305   $159.03   $159.05   $159.00  
  Purchase #4 $217.68   7.369%   $233.7208   $233.72   $233.70   $233.70  
  Purchase #5 $239.80   7.753%   $258.3917   $258.39   $258.40   $258.40  
  Purchase #6 $228.76   12.118%   $256.4811   $256.48   $256.50   $256.50  
  Purchase #7 $110.94   6.398%   $118.0379   $118.04   $118.05   $118.00  
  7 purchase totals = $1,087.99       $1,194.3672   $1,194.36   $1,194.40   $1,194.30