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 $246.37   11.313%   $274.2418   $274.24   $274.25   $274.20  
  Purchase #2 $179.54   12.535%   $202.0453   $202.05   $202.05   $202.00  
  Purchase #3 $178.81   10.586%   $197.7388   $197.74   $197.75   $197.70  
  Purchase #4 $28.76   7.112%   $30.8054   $30.81   $30.80   $30.80  
  Purchase #5 $124.53   5.594%   $131.4962   $131.50   $131.50   $131.50  
  Purchase #6 $184.71   11.422%   $205.8076   $205.81   $205.80   $205.80  
  Purchase #7 $42.60   3.443%   $44.0667   $44.07   $44.05   $44.10  
  7 purchase totals = $985.32       $1,086.2018   $1,086.22   $1,086.20   $1,086.10