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	$88.62	12.317%	$99.5353	$99.54	$99.55	$99.50
Purchase #2	$83.42	3.681%	$86.4907	$86.49	$86.50	$86.50
Purchase #3	$33.34	11.339%	$37.1204	$37.12	$37.10	$37.10
Purchase #4	$154.49	4.300%	$161.1331	$161.13	$161.15	$161.10
Purchase #5	$169.46	11.402%	$188.7818	$188.78	$188.80	$188.80
Purchase #6	$235.26	13.602%	$267.2601	$267.26	$267.25	$267.30
Purchase #7	$31.54	5.136%	$33.1599	$33.16	$33.15	$33.20
7 purchase totals =	$796.13		$873.4813	$873.48	$873.50	$873.50