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 $71.63   6.552%   $76.3232   $76.32   $76.30   $76.30  
  Purchase #2 $110.43   3.319%   $114.0952   $114.10   $114.10   $114.10  
  Purchase #3 $196.84   11.493%   $219.4628   $219.46   $219.45   $219.50  
  Purchase #4 $191.76   7.268%   $205.6971   $205.70   $205.70   $205.70  
  Purchase #5 $142.98   10.436%   $157.9014   $157.90   $157.90   $157.90  
  Purchase #6 $87.69   7.791%   $94.5219   $94.52   $94.50   $94.50  
  Purchase #7 $137.81   13.525%   $156.4488   $156.45   $156.45   $156.40  
  7 purchase totals = $939.14       $1,024.4504   $1,024.45   $1,024.40   $1,024.40