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	$202.51	4.109%	$210.8311	$210.83	$210.85	$210.80
Purchase #2	$65.46	8.293%	$70.8886	$70.89	$70.90	$70.90
Purchase #3	$207.29	11.864%	$231.8829	$231.88	$231.90	$231.90
Purchase #4	$224.74	6.102%	$238.4536	$238.45	$238.45	$238.50
Purchase #5	$150.31	9.847%	$165.111	$165.11	$165.10	$165.10
Purchase #6	$197.54	9.702%	$216.7053	$216.71	$216.70	$216.70
Purchase #7	$119.30	3.329%	$123.2715	$123.27	$123.25	$123.30
7 purchase totals =	$1,167.15		$1,257.1440	$1,257.14	$1,257.15	$1,257.20