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 $206.58   13.600%   $234.6749   $234.67   $234.65   $234.70  
  Purchase #2 $114.99   6.845%   $122.8611   $122.86   $122.85   $122.90  
  Purchase #3 $242.90   6.834%   $259.4998   $259.50   $259.50   $259.50  
  Purchase #4 $231.74   6.576%   $246.9792   $246.98   $247.00   $247.00  
  Purchase #5 $42.79   10.511%   $47.2877   $47.29   $47.30   $47.30  
  Purchase #6 $72.99   13.124%   $82.5692   $82.57   $82.55   $82.60  
  Purchase #7 $92.30   9.865%   $101.4054   $101.41   $101.40   $101.40  
  7 purchase totals = $1,004.29       $1,095.2773   $1,095.28   $1,095.25   $1,095.40