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 $66.63   5.450%   $70.2613   $70.26   $70.25   $70.30  
  Purchase #2 $241.93   9.558%   $265.0537   $265.05   $265.05   $265.10  
  Purchase #3 $155.72   8.287%   $168.6245   $168.62   $168.60   $168.60  
  Purchase #4 $230.55   11.620%   $257.3399   $257.34   $257.35   $257.30  
  Purchase #5 $128.54   4.848%   $134.7716   $134.77   $134.75   $134.80  
  Purchase #6 $95.90   12.404%   $107.7954   $107.80   $107.80   $107.80  
  Purchase #7 $62.32   7.197%   $66.8052   $66.81   $66.80   $66.80  
  7 purchase totals = $981.59       $1,070.6516   $1,070.65   $1,070.60   $1,070.70