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	$31.65	4.604%	$33.1072	$33.11	$33.10	$33.10
Purchase #2	$28.93	8.242%	$31.3144	$31.31	$31.30	$31.30
Purchase #3	$56.33	10.436%	$62.2086	$62.21	$62.20	$62.20
Purchase #4	$80.89	12.205%	$90.7626	$90.76	$90.75	$90.80
Purchase #5	$64.41	10.180%	$70.9669	$70.97	$70.95	$71.00
Purchase #6	$36.95	11.795%	$41.3083	$41.31	$41.30	$41.30
Purchase #7	$177.92	3.718%	$184.5351	$184.54	$184.55	$184.50
7 purchase totals =	$477.08		$514.2031	$514.21	$514.15	$514.20