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 $62.86   10.211%   $69.2786   $69.28   $69.30   $69.30  
  Purchase #2 $108.63   6.448%   $115.6345   $115.63   $115.65   $115.60  
  Purchase #3 $224.93   7.231%   $241.1947   $241.19   $241.20   $241.20  
  Purchase #4 $97.46   9.873%   $107.0822   $107.08   $107.10   $107.10  
  Purchase #5 $226.68   3.571%   $234.7747   $234.77   $234.75   $234.80  
  Purchase #6 $84.42   8.722%   $91.7831   $91.78   $91.80   $91.80  
  Purchase #7 $104.79   4.661%   $109.6743   $109.67   $109.65   $109.70  
  7 purchase totals = $909.77       $969.4221   $969.40   $969.45   $969.50