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 $115.95   8.296%   $125.5692   $125.57   $125.55   $125.60  
  Purchase #2 $70.30   8.358%   $76.1757   $76.18   $76.20   $76.20  
  Purchase #3 $205.39   8.521%   $222.8913   $222.89   $222.90   $222.90  
  Purchase #4 $110.57   8.736%   $120.2294   $120.23   $120.25   $120.20  
  Purchase #5 $204.95   6.606%   $218.489   $218.49   $218.50   $218.50  
  Purchase #6 $46.70   12.558%   $52.5646   $52.56   $52.55   $52.60  
  Purchase #7 $61.90   6.371%   $65.8436   $65.84   $65.85   $65.80  
  7 purchase totals = $815.76       $881.7628   $881.76   $881.80   $881.80