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 $215.96   13.778%   $245.715   $245.72   $245.70   $245.70  
  Purchase #2 $106.31   11.253%   $118.2731   $118.27   $118.25   $118.30  
  Purchase #3 $48.90   5.692%   $51.6834   $51.68   $51.70   $51.70  
  Purchase #4 $25.47   4.786%   $26.689   $26.69   $26.70   $26.70  
  Purchase #5 $105.25   9.466%   $115.213   $115.21   $115.20   $115.20  
  Purchase #6 $216.69   6.208%   $230.1421   $230.14   $230.15   $230.10  
  Purchase #7 $153.98   12.126%   $172.6516   $172.65   $172.65   $172.70  
  7 purchase totals = $872.56       $960.3672   $960.36   $960.35   $960.40