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	$217.37	5.373%	$229.0493	$229.05	$229.05	$229.00
Purchase #2	$175.95	6.155%	$186.7797	$186.78	$186.80	$186.80
Purchase #3	$35.92	11.129%	$39.9175	$39.92	$39.90	$39.90
Purchase #4	$172.83	9.777%	$189.7276	$189.73	$189.75	$189.70
Purchase #5	$147.68	10.253%	$162.8216	$162.82	$162.80	$162.80
Purchase #6	$37.79	13.604%	$42.931	$42.93	$42.95	$42.90
Purchase #7	$80.83	5.499%	$85.2748	$85.27	$85.25	$85.30
7 purchase totals =	$868.37		$936.5015	$936.50	$936.50	$936.40