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 $17.57   7.388%   $18.8681   $18.87   $18.85   $18.90  
  Purchase #2 $203.56   5.324%   $214.3975   $214.40   $214.40   $214.40  
  Purchase #3 $197.54   8.810%   $214.9433   $214.94   $214.95   $214.90  
  Purchase #4 $173.67   6.545%   $185.0367   $185.04   $185.05   $185.00  
  Purchase #5 $19.56   9.279%   $21.375   $21.38   $21.40   $21.40  
  Purchase #6 $243.81   10.468%   $269.332   $269.33   $269.35   $269.30  
  Purchase #7 $190.80   7.671%   $205.4363   $205.44   $205.45   $205.40  
  7 purchase totals = $1,046.51       $1,129.3889   $1,129.40   $1,129.45   $1,129.30