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 $224.56   13.824%   $255.6032   $255.60   $255.60   $255.60  
  Purchase #2 $212.74   3.525%   $220.2391   $220.24   $220.25   $220.20  
  Purchase #3 $203.48   5.350%   $214.3662   $214.37   $214.35   $214.40  
  Purchase #4 $70.74   4.230%   $73.7323   $73.73   $73.75   $73.70  
  Purchase #5 $153.37   6.455%   $163.27   $163.27   $163.25   $163.30  
  Purchase #6 $173.35   10.131%   $190.9121   $190.91   $190.90   $190.90  
  Purchase #7 $129.25   3.765%   $134.1163   $134.12   $134.10   $134.10  
  7 purchase totals = $1,167.49       $1,252.2392   $1,252.24   $1,252.20   $1,252.20