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 $208.67   12.416%   $234.5785   $234.58   $234.60   $234.60  
  Purchase #2 $114.33   8.730%   $124.311   $124.31   $124.30   $124.30  
  Purchase #3 $185.39   10.162%   $204.2293   $204.23   $204.25   $204.20  
  Purchase #4 $138.29   10.215%   $152.4163   $152.42   $152.40   $152.40  
  Purchase #5 $194.68   6.635%   $207.597   $207.60   $207.60   $207.60  
  Purchase #6 $163.80   8.476%   $177.6837   $177.68   $177.70   $177.70  
  Purchase #7 $16.59   13.197%   $18.7794   $18.78   $18.80   $18.80  
  7 purchase totals = $1,021.75       $1,119.5952   $1,119.60   $1,119.65   $1,119.60