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	$25.40	13.710%	$28.8823	$28.88	$28.90	$28.90
Purchase #2	$62.33	4.480%	$65.1224	$65.12	$65.10	$65.10
Purchase #3	$187.98	4.621%	$196.6666	$196.67	$196.65	$196.70
Purchase #4	$159.48	4.555%	$166.7443	$166.74	$166.75	$166.70
Purchase #5	$77.36	10.314%	$85.3389	$85.34	$85.35	$85.30
Purchase #6	$158.93	4.758%	$166.4919	$166.49	$166.50	$166.50
Purchase #7	$151.68	12.830%	$171.1405	$171.14	$171.15	$171.10
7 purchase totals =	$823.16		$880.3869	$880.38	$880.40	$880.30