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 $180.58   13.534%   $205.0197   $205.02   $205.00   $205.00  
  Purchase #2 $236.98   12.645%   $266.9461   $266.95   $266.95   $266.90  
  Purchase #3 $127.54   6.382%   $135.6796   $135.68   $135.70   $135.70  
  Purchase #4 $184.43   3.402%   $190.7043   $190.70   $190.70   $190.70  
  Purchase #5 $131.63   3.686%   $136.4819   $136.48   $136.50   $136.50  
  Purchase #6 $12.47   10.114%   $13.7312   $13.73   $13.75   $13.70  
  Purchase #7 $203.35   10.102%   $223.8924   $223.89   $223.90   $223.90  
  7 purchase totals = $1,076.98       $1,172.4552   $1,172.45   $1,172.50   $1,172.40