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	$96.79	3.109%	$99.7992	$99.80	$99.80	$99.80
Purchase #2	$93.40	3.302%	$96.4841	$96.48	$96.50	$96.50
Purchase #3	$142.74	11.187%	$158.7083	$158.71	$158.70	$158.70
Purchase #4	$234.42	6.771%	$250.2926	$250.29	$250.30	$250.30
Purchase #5	$54.75	8.356%	$59.3249	$59.32	$59.30	$59.30
Purchase #6	$118.48	10.274%	$130.6526	$130.65	$130.65	$130.70
Purchase #7	$245.59	11.665%	$274.2381	$274.24	$274.25	$274.20
7 purchase totals =	$986.17		$1,069.4998	$1,069.49	$1,069.50	$1,069.50