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	$159.97	12.590%	$180.1102	$180.11	$180.10	$180.10
Purchase #2	$95.87	3.740%	$99.4555	$99.46	$99.45	$99.50
Purchase #3	$90.46	8.145%	$97.828	$97.83	$97.85	$97.80
Purchase #4	$46.60	8.121%	$50.3844	$50.38	$50.40	$50.40
Purchase #5	$203.81	3.279%	$210.4929	$210.49	$210.50	$210.50
Purchase #6	$53.59	10.804%	$59.3799	$59.38	$59.40	$59.40
Purchase #7	$50.67	4.747%	$53.0753	$53.08	$53.10	$53.10
7 purchase totals =	$700.97		$750.7262	$750.73	$750.80	$750.80