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 $102.64   6.487%   $109.2983   $109.30   $109.30   $109.30  
  Purchase #2 $238.58   7.125%   $255.5788   $255.58   $255.60   $255.60  
  Purchase #3 $78.45   3.473%   $81.1746   $81.17   $81.15   $81.20  
  Purchase #4 $69.79   13.543%   $79.2417   $79.24   $79.25   $79.20  
  Purchase #5 $126.39   3.237%   $130.4812   $130.48   $130.50   $130.50  
  Purchase #6 $9.40   6.240%   $9.9866   $9.99   $10.00   $10.00  
  Purchase #7 $5.49   9.416%   $6.0069   $6.01   $6.00   $6.00  
  7 purchase totals = $630.74       $671.7681   $671.77   $671.80   $671.80