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	$96.78	3.171%	$99.8489	$99.85	$99.85	$99.80
Purchase #2	$36.25	11.760%	$40.513	$40.51	$40.50	$40.50
Purchase #3	$38.78	12.192%	$43.5081	$43.51	$43.50	$43.50
Purchase #4	$79.63	13.160%	$90.1093	$90.11	$90.10	$90.10
Purchase #5	$73.74	7.725%	$79.4364	$79.44	$79.45	$79.40
Purchase #6	$92.96	4.136%	$96.8048	$96.80	$96.80	$96.80
Purchase #7	$140.94	9.481%	$154.3025	$154.30	$154.30	$154.30
7 purchase totals =	$559.08		$604.5230	$604.52	$604.50	$604.40