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	$53.62	7.844%	$57.826	$57.83	$57.85	$57.80
Purchase #2	$217.50	3.641%	$225.4192	$225.42	$225.40	$225.40
Purchase #3	$216.73	3.559%	$224.4434	$224.44	$224.45	$224.40
Purchase #4	$40.25	11.170%	$44.7459	$44.75	$44.75	$44.70
Purchase #5	$25.61	7.459%	$27.5202	$27.52	$27.50	$27.50
Purchase #6	$229.45	11.306%	$255.3916	$255.39	$255.40	$255.40
Purchase #7	$152.94	8.251%	$165.5591	$165.56	$165.55	$165.60
7 purchase totals =	$936.10		$1,000.9054	$1,000.91	$1,000.90	$1,000.80