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	$135.52	5.436%	$142.8869	$142.89	$142.90	$142.90
Purchase #2	$79.60	13.782%	$90.5705	$90.57	$90.55	$90.60
Purchase #3	$200.30	12.275%	$224.8868	$224.89	$224.90	$224.90
Purchase #4	$90.63	9.839%	$99.5471	$99.55	$99.55	$99.50
Purchase #5	$50.90	8.536%	$55.2448	$55.24	$55.25	$55.20
Purchase #6	$183.46	5.672%	$193.8659	$193.87	$193.85	$193.90
Purchase #7	$232.94	3.501%	$241.0952	$241.10	$241.10	$241.10
7 purchase totals =	$973.35		$1,048.0972	$1,048.11	$1,048.10	$1,048.10