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 $243.54   10.553%   $269.2408   $269.24   $269.25   $269.20  
  Purchase #2 $56.66   13.147%   $64.1091   $64.11   $64.10   $64.10  
  Purchase #3 $32.62   6.813%   $34.8424   $34.84   $34.85   $34.80  
  Purchase #4 $94.74   3.498%   $98.054   $98.05   $98.05   $98.10  
  Purchase #5 $121.70   4.795%   $127.5355   $127.54   $127.55   $127.50  
  Purchase #6 $229.53   6.507%   $244.4655   $244.47   $244.45   $244.50  
  Purchase #7 $41.56   6.815%   $44.3923   $44.39   $44.40   $44.40  
  7 purchase totals = $820.35       $882.6396   $882.64   $882.65   $882.60