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 $183.70   12.251%   $206.2051   $206.21   $206.20   $206.20  
  Purchase #2 $60.97   3.823%   $63.3009   $63.30   $63.30   $63.30  
  Purchase #3 $185.64   3.789%   $192.6739   $192.67   $192.65   $192.70  
  Purchase #4 $247.31   7.311%   $265.3908   $265.39   $265.40   $265.40  
  Purchase #5 $31.99   5.814%   $33.8499   $33.85   $33.85   $33.80  
  Purchase #6 $159.99   8.852%   $174.1523   $174.15   $174.15   $174.20  
  Purchase #7 $225.79   6.599%   $240.6899   $240.69   $240.70   $240.70  
  7 purchase totals = $1,095.39       $1,176.2628   $1,176.26   $1,176.25   $1,176.30