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 $51.92   8.331%   $56.2455   $56.25   $56.25   $56.20  
  Purchase #2 $239.92   8.152%   $259.4783   $259.48   $259.50   $259.50  
  Purchase #3 $168.57   4.713%   $176.5147   $176.51   $176.50   $176.50  
  Purchase #4 $15.74   10.363%   $17.3711   $17.37   $17.35   $17.40  
  Purchase #5 $91.39   5.804%   $96.6943   $96.69   $96.70   $96.70  
  Purchase #6 $205.41   12.566%   $231.2218   $231.22   $231.20   $231.20  
  Purchase #7 $173.81   5.390%   $183.1784   $183.18   $183.20   $183.20  
  7 purchase totals = $946.76       $1,020.7041   $1,020.70   $1,020.70   $1,020.70