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	$170.43	7.364%	$182.9805	$182.98	$183.00	$183.00
Purchase #2	$123.37	4.743%	$129.2214	$129.22	$129.20	$129.20
Purchase #3	$150.75	13.765%	$171.5007	$171.50	$171.50	$171.50
Purchase #4	$127.36	9.513%	$139.4758	$139.48	$139.50	$139.50
Purchase #5	$131.58	3.780%	$136.5537	$136.55	$136.55	$136.60
Purchase #6	$213.32	7.643%	$229.624	$229.62	$229.60	$229.60
Purchase #7	$220.53	5.706%	$233.1134	$233.11	$233.10	$233.10
7 purchase totals =	$1,137.34		$1,222.4695	$1,222.46	$1,222.45	$1,222.50