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	$97.57	8.312%	$105.68	$105.68	$105.70	$105.70
Purchase #2	$174.69	8.153%	$188.9325	$188.93	$188.95	$188.90
Purchase #3	$163.52	6.179%	$173.6239	$173.62	$173.60	$173.60
Purchase #4	$38.89	12.818%	$43.8749	$43.87	$43.85	$43.90
Purchase #5	$196.32	7.805%	$211.6428	$211.64	$211.65	$211.60
Purchase #6	$71.85	9.322%	$78.5479	$78.55	$78.55	$78.50
Purchase #7	$182.84	3.159%	$188.6159	$188.62	$188.60	$188.60
7 purchase totals =	$925.68		$990.9179	$990.91	$990.90	$990.80