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	$76.65	6.316%	$81.4912	$81.49	$81.50	$81.50
Purchase #2	$72.43	8.571%	$78.638	$78.64	$78.65	$78.60
Purchase #3	$110.53	11.596%	$123.3471	$123.35	$123.35	$123.30
Purchase #4	$64.92	7.166%	$69.5722	$69.57	$69.55	$69.60
Purchase #5	$119.92	13.767%	$136.4294	$136.43	$136.45	$136.40
Purchase #6	$246.49	7.312%	$264.5133	$264.51	$264.50	$264.50
Purchase #7	$73.78	9.796%	$81.0075	$81.01	$81.00	$81.00
7 purchase totals =	$764.72		$834.9987	$835.00	$835.00	$834.90