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	$90.78	9.307%	$99.2289	$99.23	$99.25	$99.20
Purchase #2	$56.71	7.687%	$61.0693	$61.07	$61.05	$61.10
Purchase #3	$146.78	6.457%	$156.2576	$156.26	$156.25	$156.30
Purchase #4	$215.41	5.470%	$227.1929	$227.19	$227.20	$227.20
Purchase #5	$33.34	5.454%	$35.1584	$35.16	$35.15	$35.20
Purchase #6	$114.59	6.390%	$121.9123	$121.91	$121.90	$121.90
Purchase #7	$31.34	6.860%	$33.4899	$33.49	$33.50	$33.50
7 purchase totals =	$688.95		$734.3093	$734.31	$734.30	$734.40