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	$56.28	6.262%	$59.8043	$59.80	$59.80	$59.80
Purchase #2	$156.61	9.132%	$170.9116	$170.91	$170.90	$170.90
Purchase #3	$47.89	13.267%	$54.2436	$54.24	$54.25	$54.20
Purchase #4	$86.51	3.188%	$89.2679	$89.27	$89.25	$89.30
Purchase #5	$79.67	13.873%	$90.7226	$90.72	$90.70	$90.70
Purchase #6	$59.56	8.778%	$64.7882	$64.79	$64.80	$64.80
Purchase #7	$31.29	6.319%	$33.2672	$33.27	$33.25	$33.30
7 purchase totals =	$517.81		$563.0054	$563.00	$562.95	$563.00