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 $194.44   13.119%   $219.9486   $219.95   $219.95   $219.90  
  Purchase #2 $184.45   11.581%   $205.8112   $205.81   $205.80   $205.80  
  Purchase #3 $91.42   11.840%   $102.2441   $102.24   $102.25   $102.20  
  Purchase #4 $239.27   13.611%   $271.837   $271.84   $271.85   $271.80  
  Purchase #5 $158.47   11.230%   $176.2662   $176.27   $176.25   $176.30  
  Purchase #6 $203.67   9.305%   $222.6215   $222.62   $222.60   $222.60  
  Purchase #7 $185.59   11.548%   $207.0219   $207.02   $207.00   $207.00  
  7 purchase totals = $1,257.31       $1,405.7505   $1,405.75   $1,405.70   $1,405.60