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	$159.83	3.590%	$165.5679	$165.57	$165.55	$165.60
Purchase #2	$199.47	12.240%	$223.8851	$223.89	$223.90	$223.90
Purchase #3	$169.98	8.860%	$185.0402	$185.04	$185.05	$185.00
Purchase #4	$58.82	9.553%	$64.4391	$64.44	$64.45	$64.40
Purchase #5	$190.67	10.433%	$210.5626	$210.56	$210.55	$210.60
Purchase #6	$172.69	5.384%	$181.9876	$181.99	$182.00	$182.00
Purchase #7	$49.43	10.715%	$54.7264	$54.73	$54.75	$54.70
7 purchase totals =	$1,000.89		$1,086.2089	$1,086.22	$1,086.25	$1,086.20