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	$136.93	12.364%	$153.86	$153.86	$153.85	$153.90
Purchase #2	$110.34	11.536%	$123.0688	$123.07	$123.05	$123.10
Purchase #3	$40.92	11.594%	$45.6643	$45.66	$45.65	$45.70
Purchase #4	$151.39	12.122%	$169.7415	$169.74	$169.75	$169.70
Purchase #5	$95.90	9.400%	$104.9146	$104.91	$104.90	$104.90
Purchase #6	$201.55	8.842%	$219.3711	$219.37	$219.35	$219.40
Purchase #7	$55.40	4.583%	$57.939	$57.94	$57.95	$57.90
7 purchase totals =	$792.43		$874.5593	$874.55	$874.50	$874.60