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 $126.91   11.786%   $141.8676   $141.87   $141.85   $141.90  
  Purchase #2 $65.55   11.823%   $73.3   $73.30   $73.30   $73.30  
  Purchase #3 $201.93   5.266%   $212.5636   $212.56   $212.55   $212.60  
  Purchase #4 $163.82   13.154%   $185.3689   $185.37   $185.35   $185.40  
  Purchase #5 $231.85   13.409%   $262.9388   $262.94   $262.95   $262.90  
  Purchase #6 $189.76   4.712%   $198.7015   $198.70   $198.70   $198.70  
  Purchase #7 $200.41   9.670%   $219.7896   $219.79   $219.80   $219.80  
  7 purchase totals = $1,180.23       $1,294.5300   $1,294.53   $1,294.50   $1,294.60