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	$112.41	7.257%	$120.5676	$120.57	$120.55	$120.60
Purchase #2	$231.73	10.150%	$255.2506	$255.25	$255.25	$255.30
Purchase #3	$23.50	6.565%	$25.0428	$25.04	$25.05	$25.00
Purchase #4	$194.30	12.764%	$219.1005	$219.10	$219.10	$219.10
Purchase #5	$162.79	6.636%	$173.5927	$173.59	$173.60	$173.60
Purchase #6	$143.71	12.419%	$161.5573	$161.56	$161.55	$161.60
Purchase #7	$45.74	4.702%	$47.8907	$47.89	$47.90	$47.90
7 purchase totals =	$914.18		$1,003.0022	$1,003.00	$1,003.00	$1,003.10