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 $223.42   7.863%   $240.9875   $240.99   $241.00   $241.00  
  Purchase #2 $169.53   8.653%   $184.1994   $184.20   $184.20   $184.20  
  Purchase #3 $92.86   13.747%   $105.6255   $105.63   $105.65   $105.60  
  Purchase #4 $186.32   6.413%   $198.2687   $198.27   $198.25   $198.30  
  Purchase #5 $135.44   4.662%   $141.7542   $141.75   $141.75   $141.80  
  Purchase #6 $35.95   5.768%   $38.0236   $38.02   $38.00   $38.00  
  Purchase #7 $155.40   13.263%   $176.0107   $176.01   $176.00   $176.00  
  7 purchase totals = $998.92       $1,084.8696   $1,084.87   $1,084.85   $1,084.90