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	$192.74	3.510%	$199.5052	$199.51	$199.50	$199.50
Purchase #2	$50.48	11.388%	$56.2287	$56.23	$56.25	$56.20
Purchase #3	$81.69	10.811%	$90.5215	$90.52	$90.50	$90.50
Purchase #4	$150.73	3.577%	$156.1216	$156.12	$156.10	$156.10
Purchase #5	$101.39	3.466%	$104.9042	$104.90	$104.90	$104.90
Purchase #6	$64.38	7.574%	$69.2561	$69.26	$69.25	$69.30
Purchase #7	$61.33	11.285%	$68.2511	$68.25	$68.25	$68.30
7 purchase totals =	$702.74		$744.7884	$744.79	$744.75	$744.80