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 $214.81   8.151%   $232.3192   $232.32   $232.30   $232.30  
  Purchase #2 $233.84   7.124%   $250.4988   $250.50   $250.50   $250.50  
  Purchase #3 $9.48   10.754%   $10.4995   $10.50   $10.50   $10.50  
  Purchase #4 $183.84   8.494%   $199.4554   $199.46   $199.45   $199.50  
  Purchase #5 $203.70   5.263%   $214.4207   $214.42   $214.40   $214.40  
  Purchase #6 $147.66   6.225%   $156.8518   $156.85   $156.85   $156.90  
  Purchase #7 $144.56   10.222%   $159.3369   $159.34   $159.35   $159.30  
  7 purchase totals = $1,137.89       $1,223.3823   $1,223.39   $1,223.35   $1,223.40