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	$157.79	13.796%	$179.5587	$179.56	$179.55	$179.60
Purchase #2	$28.40	13.623%	$32.2689	$32.27	$32.25	$32.30
Purchase #3	$124.77	5.184%	$131.2381	$131.24	$131.25	$131.20
Purchase #4	$42.47	10.196%	$46.8002	$46.80	$46.80	$46.80
Purchase #5	$79.89	7.247%	$85.6796	$85.68	$85.70	$85.70
Purchase #6	$27.72	12.354%	$31.1445	$31.14	$31.15	$31.10
Purchase #7	$88.88	6.631%	$94.7736	$94.77	$94.75	$94.80
7 purchase totals =	$549.92		$601.4636	$601.46	$601.45	$601.50