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 $246.51   9.186%   $269.1544   $269.15   $269.15   $269.20  
  Purchase #2 $246.27   5.395%   $259.5563   $259.56   $259.55   $259.60  
  Purchase #3 $47.91   5.317%   $50.4574   $50.46   $50.45   $50.50  
  Purchase #4 $117.56   5.788%   $124.3644   $124.36   $124.35   $124.40  
  Purchase #5 $113.44   12.341%   $127.4396   $127.44   $127.45   $127.40  
  Purchase #6 $189.27   9.316%   $206.9024   $206.90   $206.90   $206.90  
  Purchase #7 $109.77   10.329%   $121.1081   $121.11   $121.10   $121.10  
  7 purchase totals = $1,070.73       $1,158.9826   $1,158.98   $1,158.95   $1,159.10