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 $58.48   11.495%   $65.2023   $65.20   $65.20   $65.20  
  Purchase #2 $119.56   3.515%   $123.7625   $123.76   $123.75   $123.80  
  Purchase #3 $143.55   6.302%   $152.5965   $152.60   $152.60   $152.60  
  Purchase #4 $235.76   5.780%   $249.3869   $249.39   $249.40   $249.40  
  Purchase #5 $130.54   7.177%   $139.9089   $139.91   $139.90   $139.90  
  Purchase #6 $170.66   12.812%   $192.525   $192.53   $192.55   $192.50  
  Purchase #7 $162.99   13.237%   $184.565   $184.57   $184.55   $184.60  
  7 purchase totals = $1,021.54       $1,107.9471   $1,107.96   $1,107.95   $1,108.00