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	$165.49	13.616%	$188.0231	$188.02	$188.00	$188.00
Purchase #2	$131.25	4.163%	$136.7139	$136.71	$136.70	$136.70
Purchase #3	$205.50	8.276%	$222.5072	$222.51	$222.50	$222.50
Purchase #4	$31.62	9.836%	$34.7301	$34.73	$34.75	$34.70
Purchase #5	$139.38	7.743%	$150.1722	$150.17	$150.15	$150.20
Purchase #6	$246.27	6.109%	$261.3146	$261.31	$261.30	$261.30
Purchase #7	$84.60	7.327%	$90.7986	$90.80	$90.80	$90.80
7 purchase totals =	$1,004.11		$1,084.2597	$1,084.25	$1,084.20	$1,084.20