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 $238.46   6.386%   $253.6881   $253.69   $253.70   $253.70  
  Purchase #2 $162.37   8.529%   $176.2185   $176.22   $176.20   $176.20  
  Purchase #3 $98.93   7.277%   $106.1291   $106.13   $106.15   $106.10  
  Purchase #4 $68.54   3.205%   $70.7367   $70.74   $70.75   $70.70  
  Purchase #5 $156.33   7.397%   $167.8937   $167.89   $167.90   $167.90  
  Purchase #6 $26.89   6.126%   $28.5373   $28.54   $28.55   $28.50  
  Purchase #7 $153.26   6.834%   $163.7338   $163.73   $163.75   $163.70  
  7 purchase totals = $904.78       $966.9372   $966.94   $967.00   $966.80