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 $119.64   11.722%   $133.6642   $133.66   $133.65   $133.70  
  Purchase #2 $81.57   11.126%   $90.6455   $90.65   $90.65   $90.60  
  Purchase #3 $148.30   11.730%   $165.6956   $165.70   $165.70   $165.70  
  Purchase #4 $178.59   9.451%   $195.4685   $195.47   $195.45   $195.50  
  Purchase #5 $77.36   13.602%   $87.8825   $87.88   $87.90   $87.90  
  Purchase #6 $248.99   11.233%   $276.959   $276.96   $276.95   $277.00  
  Purchase #7 $121.90   7.179%   $130.6512   $130.65   $130.65   $130.70  
  7 purchase totals = $976.35       $1,080.9665   $1,080.97   $1,080.95   $1,081.10