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 $204.25   6.436%   $217.3955   $217.40   $217.40   $217.40  
  Purchase #2 $174.90   13.413%   $198.3593   $198.36   $198.35   $198.40  
  Purchase #3 $177.98   11.411%   $198.2893   $198.29   $198.30   $198.30  
  Purchase #4 $55.44   8.833%   $60.337   $60.34   $60.35   $60.30  
  Purchase #5 $196.79   5.527%   $207.6666   $207.67   $207.65   $207.70  
  Purchase #6 $118.93   9.798%   $130.5828   $130.58   $130.60   $130.60  
  Purchase #7 $210.42   11.288%   $234.1722   $234.17   $234.15   $234.20  
  7 purchase totals = $1,138.71       $1,246.8027   $1,246.81   $1,246.80   $1,246.90