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 $212.69   4.498%   $222.2568   $222.26   $222.25   $222.30  
  Purchase #2 $183.79   7.146%   $196.9236   $196.92   $196.90   $196.90  
  Purchase #3 $165.64   8.447%   $179.6316   $179.63   $179.65   $179.60  
  Purchase #4 $168.61   7.563%   $181.362   $181.36   $181.35   $181.40  
  Purchase #5 $241.71   10.328%   $266.6738   $266.67   $266.65   $266.70  
  Purchase #6 $26.80   9.467%   $29.3372   $29.34   $29.35   $29.30  
  Purchase #7 $170.79   11.271%   $190.0397   $190.04   $190.05   $190.00  
  7 purchase totals = $1,170.03       $1,266.2247   $1,266.22   $1,266.20   $1,266.20