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 $63.44   13.824%   $72.2099   $72.21   $72.20   $72.20  
  Purchase #2 $116.58   12.397%   $131.0324   $131.03   $131.05   $131.00  
  Purchase #3 $82.59   4.313%   $86.1521   $86.15   $86.15   $86.20  
  Purchase #4 $73.66   5.269%   $77.5411   $77.54   $77.55   $77.50  
  Purchase #5 $236.30   8.337%   $256.0003   $256.00   $256.00   $256.00  
  Purchase #6 $152.81   11.199%   $169.9232   $169.92   $169.90   $169.90  
  Purchase #7 $222.97   8.278%   $241.4275   $241.43   $241.45   $241.40  
  7 purchase totals = $948.35       $1,034.2865   $1,034.28   $1,034.30   $1,034.20