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 $184.89   5.614%   $195.2697   $195.27   $195.25   $195.30  
  Purchase #2 $54.48   12.527%   $61.3047   $61.30   $61.30   $61.30  
  Purchase #3 $250.99   8.563%   $272.4823   $272.48   $272.50   $272.50  
  Purchase #4 $61.57   7.791%   $66.3669   $66.37   $66.35   $66.40  
  Purchase #5 $194.54   6.805%   $207.7784   $207.78   $207.80   $207.80  
  Purchase #6 $223.63   11.497%   $249.3407   $249.34   $249.35   $249.30  
  Purchase #7 $198.60   3.435%   $205.4219   $205.42   $205.40   $205.40  
  7 purchase totals = $1,168.70       $1,257.9646   $1,257.96   $1,257.95   $1,258.00