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 $113.89   10.581%   $125.9407   $125.94   $125.95   $125.90  
  Purchase #2 $64.84   7.430%   $69.6576   $69.66   $69.65   $69.70  
  Purchase #3 $204.69   10.838%   $226.8743   $226.87   $226.85   $226.90  
  Purchase #4 $39.28   12.175%   $44.0623   $44.06   $44.05   $44.10  
  Purchase #5 $214.83   8.685%   $233.488   $233.49   $233.50   $233.50  
  Purchase #6 $49.89   12.809%   $56.2804   $56.28   $56.30   $56.30  
  Purchase #7 $85.82   12.504%   $96.5509   $96.55   $96.55   $96.60  
  7 purchase totals = $773.24       $852.8542   $852.85   $852.85   $853.00