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	$79.46	5.491%	$83.8231	$83.82	$83.80	$83.80
Purchase #2	$90.77	12.132%	$101.7822	$101.78	$101.80	$101.80
Purchase #3	$242.86	13.114%	$274.7087	$274.71	$274.70	$274.70
Purchase #4	$62.62	7.237%	$67.1518	$67.15	$67.15	$67.20
Purchase #5	$245.95	6.218%	$261.2432	$261.24	$261.25	$261.20
Purchase #6	$61.65	6.190%	$65.4661	$65.47	$65.45	$65.50
Purchase #7	$75.40	13.471%	$85.5571	$85.56	$85.55	$85.60
7 purchase totals =	$858.71		$939.7322	$939.73	$939.70	$939.80