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	$249.57	13.193%	$282.4958	$282.50	$282.50	$282.50
Purchase #2	$43.41	12.506%	$48.8389	$48.84	$48.85	$48.80
Purchase #3	$204.49	5.479%	$215.694	$215.69	$215.70	$215.70
Purchase #4	$165.54	3.232%	$170.8903	$170.89	$170.90	$170.90
Purchase #5	$50.34	13.582%	$57.1772	$57.18	$57.20	$57.20
Purchase #6	$90.78	12.471%	$102.1012	$102.10	$102.10	$102.10
Purchase #7	$122.38	11.391%	$136.3203	$136.32	$136.30	$136.30
7 purchase totals =	$926.51		$1,013.5177	$1,013.52	$1,013.55	$1,013.50