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 $80.36   4.461%   $83.9449   $83.94   $83.95   $83.90  
  Purchase #2 $179.53   3.357%   $185.5568   $185.56   $185.55   $185.60  
  Purchase #3 $60.47   13.265%   $68.4913   $68.49   $68.50   $68.50  
  Purchase #4 $238.99   7.340%   $256.5319   $256.53   $256.55   $256.50  
  Purchase #5 $208.31   8.175%   $225.3393   $225.34   $225.35   $225.30  
  Purchase #6 $50.95   11.368%   $56.742   $56.74   $56.75   $56.70  
  Purchase #7 $111.35   11.463%   $124.1141   $124.11   $124.10   $124.10  
  7 purchase totals = $929.96       $1,000.7203   $1,000.71   $1,000.75   $1,000.60