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 $245.63   11.621%   $274.1747   $274.17   $274.15   $274.20  
  Purchase #2 $171.59   4.466%   $179.2532   $179.25   $179.25   $179.30  
  Purchase #3 $21.38   10.169%   $23.5541   $23.55   $23.55   $23.60  
  Purchase #4 $87.35   7.130%   $93.5781   $93.58   $93.60   $93.60  
  Purchase #5 $231.55   6.696%   $247.0546   $247.05   $247.05   $247.10  
  Purchase #6 $176.40   8.348%   $191.1259   $191.13   $191.15   $191.10  
  Purchase #7 $24.67   9.411%   $26.9917   $26.99   $27.00   $27.00  
  7 purchase totals = $958.57       $1,035.7323   $1,035.72   $1,035.75   $1,035.90