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 $58.55   8.788%   $63.6954   $63.70   $63.70   $63.70  
  Purchase #2 $49.93   10.391%   $55.1182   $55.12   $55.10   $55.10  
  Purchase #3 $38.86   9.456%   $42.5346   $42.53   $42.55   $42.50  
  Purchase #4 $198.87   11.825%   $222.3864   $222.39   $222.40   $222.40  
  Purchase #5 $47.84   4.164%   $49.8321   $49.83   $49.85   $49.80  
  Purchase #6 $233.74   3.195%   $241.208   $241.21   $241.20   $241.20  
  Purchase #7 $106.33   5.530%   $112.21   $112.21   $112.20   $112.20  
  7 purchase totals = $734.12       $786.9847   $786.99   $787.00   $786.90