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 $182.56   11.872%   $204.2335   $204.23   $204.25   $204.20  
  Purchase #2 $113.74   9.758%   $124.8387   $124.84   $124.85   $124.80  
  Purchase #3 $65.69   7.670%   $70.7284   $70.73   $70.75   $70.70  
  Purchase #4 $237.87   10.341%   $262.4681   $262.47   $262.45   $262.50  
  Purchase #5 $86.32   12.322%   $96.9564   $96.96   $96.95   $97.00  
  Purchase #6 $103.65   10.811%   $114.8556   $114.86   $114.85   $114.90  
  Purchase #7 $162.35   8.452%   $176.0718   $176.07   $176.05   $176.10  
  7 purchase totals = $952.18       $1,050.1525   $1,050.16   $1,050.15   $1,050.20