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 $243.81   9.718%   $267.5035   $267.50   $267.50   $267.50  
  Purchase #2 $22.86   7.654%   $24.6097   $24.61   $24.60   $24.60  
  Purchase #3 $86.58   6.333%   $92.0631   $92.06   $92.05   $92.10  
  Purchase #4 $135.85   9.397%   $148.6158   $148.62   $148.60   $148.60  
  Purchase #5 $67.83   3.285%   $70.0582   $70.06   $70.05   $70.10  
  Purchase #6 $176.25   3.736%   $182.8347   $182.83   $182.85   $182.80  
  Purchase #7 $165.84   13.664%   $188.5004   $188.50   $188.50   $188.50  
  7 purchase totals = $899.02       $974.1854   $974.18   $974.15   $974.20