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	$250.56	6.279%	$266.2927	$266.29	$266.30	$266.30
Purchase #2	$242.73	12.364%	$272.7411	$272.74	$272.75	$272.70
Purchase #3	$98.68	13.231%	$111.7364	$111.74	$111.75	$111.70
Purchase #4	$35.67	5.232%	$37.5363	$37.54	$37.55	$37.50
Purchase #5	$147.48	6.237%	$156.6783	$156.68	$156.70	$156.70
Purchase #6	$151.91	9.721%	$166.6772	$166.68	$166.70	$166.70
Purchase #7	$71.99	11.354%	$80.1637	$80.16	$80.15	$80.20
7 purchase totals =	$999.02		$1,091.8257	$1,091.83	$1,091.90	$1,091.80