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	$79.76	3.693%	$82.7055	$82.71	$82.70	$82.70
Purchase #2	$153.57	12.819%	$173.2561	$173.26	$173.25	$173.30
Purchase #3	$156.96	3.447%	$162.3704	$162.37	$162.35	$162.40
Purchase #4	$191.39	9.847%	$210.2362	$210.24	$210.25	$210.20
Purchase #5	$152.34	4.132%	$158.6347	$158.63	$158.65	$158.60
Purchase #6	$42.25	11.599%	$47.1506	$47.15	$47.15	$47.20
Purchase #7	$231.54	8.758%	$251.8183	$251.82	$251.80	$251.80
7 purchase totals =	$1,007.81		$1,086.1718	$1,086.18	$1,086.15	$1,086.20