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 $56.26   11.821%   $62.9105   $62.91   $62.90   $62.90  
  Purchase #2 $142.28   7.576%   $153.0591   $153.06   $153.05   $153.10  
  Purchase #3 $239.62   13.585%   $272.1724   $272.17   $272.15   $272.20  
  Purchase #4 $177.34   12.296%   $199.1457   $199.15   $199.15   $199.10  
  Purchase #5 $34.44   4.599%   $36.0239   $36.02   $36.00   $36.00  
  Purchase #6 $98.85   11.867%   $110.5805   $110.58   $110.60   $110.60  
  Purchase #7 $215.90   6.780%   $230.538   $230.54   $230.55   $230.50  
  7 purchase totals = $964.69       $1,064.4301   $1,064.43   $1,064.40   $1,064.40