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	$92.28	7.410%	$99.1179	$99.12	$99.10	$99.10
Purchase #2	$89.51	7.363%	$96.1006	$96.10	$96.10	$96.10
Purchase #3	$161.67	10.591%	$178.7925	$178.79	$178.80	$178.80
Purchase #4	$100.72	3.280%	$104.0236	$104.02	$104.00	$104.00
Purchase #5	$216.86	3.545%	$224.5477	$224.55	$224.55	$224.50
Purchase #6	$39.27	10.534%	$43.4067	$43.41	$43.40	$43.40
Purchase #7	$150.58	7.405%	$161.7304	$161.73	$161.75	$161.70
7 purchase totals =	$850.89		$907.7194	$907.72	$907.70	$907.60