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 $81.26   6.621%   $86.6402   $86.64   $86.65   $86.60  
  Purchase #2 $170.98   12.858%   $192.9646   $192.96   $192.95   $193.00  
  Purchase #3 $57.64   6.653%   $61.4748   $61.47   $61.45   $61.50  
  Purchase #4 $138.27   10.837%   $153.2543   $153.25   $153.25   $153.30  
  Purchase #5 $206.65   3.371%   $213.6162   $213.62   $213.60   $213.60  
  Purchase #6 $117.84   8.771%   $128.1757   $128.18   $128.20   $128.20  
  Purchase #7 $165.58   6.129%   $175.7284   $175.73   $175.75   $175.70  
  7 purchase totals = $938.22       $1,011.8542   $1,011.85   $1,011.85   $1,011.90