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	$64.29	5.287%	$67.689	$67.69	$67.70	$67.70
Purchase #2	$170.88	9.230%	$186.6522	$186.65	$186.65	$186.70
Purchase #3	$54.40	9.207%	$59.4086	$59.41	$59.40	$59.40
Purchase #4	$226.71	12.804%	$255.7379	$255.74	$255.75	$255.70
Purchase #5	$161.46	12.854%	$182.2141	$182.21	$182.20	$182.20
Purchase #6	$139.43	6.367%	$148.3075	$148.31	$148.30	$148.30
Purchase #7	$90.78	13.580%	$103.1079	$103.11	$103.10	$103.10
7 purchase totals =	$907.95		$1,003.1172	$1,003.12	$1,003.10	$1,003.10