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 $123.53   13.334%   $140.0015   $140.00   $140.00   $140.00  
  Purchase #2 $191.73   6.576%   $204.3382   $204.34   $204.35   $204.30  
  Purchase #3 $158.51   3.387%   $163.8787   $163.88   $163.90   $163.90  
  Purchase #4 $230.62   9.484%   $252.492   $252.49   $252.50   $252.50  
  Purchase #5 $28.89   3.784%   $29.9832   $29.98   $30.00   $30.00  
  Purchase #6 $199.46   3.450%   $206.3414   $206.34   $206.35   $206.30  
  Purchase #7 $182.69   11.194%   $203.1403   $203.14   $203.15   $203.10  
  7 purchase totals = $1,115.43       $1,200.1753   $1,200.17   $1,200.25   $1,200.10