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	$92.45	8.661%	$100.4571	$100.46	$100.45	$100.50
Purchase #2	$17.49	5.438%	$18.4411	$18.44	$18.45	$18.40
Purchase #3	$93.28	12.516%	$104.9549	$104.95	$104.95	$105.00
Purchase #4	$123.59	12.106%	$138.5518	$138.55	$138.55	$138.60
Purchase #5	$156.36	5.570%	$165.0693	$165.07	$165.05	$165.10
Purchase #6	$186.58	10.157%	$205.5309	$205.53	$205.55	$205.50
Purchase #7	$35.39	5.767%	$37.4309	$37.43	$37.45	$37.40
7 purchase totals =	$705.14		$770.4360	$770.43	$770.45	$770.50