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	$51.78	5.765%	$54.7651	$54.77	$54.75	$54.80
Purchase #2	$154.32	10.368%	$170.3199	$170.32	$170.30	$170.30
Purchase #3	$60.27	3.781%	$62.5488	$62.55	$62.55	$62.50
Purchase #4	$147.55	12.151%	$165.4788	$165.48	$165.50	$165.50
Purchase #5	$98.44	4.344%	$102.7162	$102.72	$102.70	$102.70
Purchase #6	$20.56	11.684%	$22.9622	$22.96	$22.95	$23.00
Purchase #7	$163.73	13.285%	$185.4815	$185.48	$185.50	$185.50
7 purchase totals =	$696.65		$764.2725	$764.28	$764.25	$764.30