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	$231.37	8.364%	$250.7218	$250.72	$250.70	$250.70
Purchase #2	$59.73	7.595%	$64.2665	$64.27	$64.25	$64.30
Purchase #3	$22.60	13.230%	$25.59	$25.59	$25.60	$25.60
Purchase #4	$135.98	7.769%	$146.5443	$146.54	$146.55	$146.50
Purchase #5	$110.28	7.761%	$118.8388	$118.84	$118.85	$118.80
Purchase #6	$54.82	11.457%	$61.1007	$61.10	$61.10	$61.10
Purchase #7	$42.63	7.424%	$45.7949	$45.79	$45.80	$45.80
7 purchase totals =	$657.41		$712.8570	$712.85	$712.85	$712.80