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	$85.41	4.306%	$89.0878	$89.09	$89.10	$89.10
Purchase #2	$146.99	10.733%	$162.7664	$162.77	$162.75	$162.80
Purchase #3	$89.40	4.629%	$93.5383	$93.54	$93.55	$93.50
Purchase #4	$198.84	7.458%	$213.6695	$213.67	$213.65	$213.70
Purchase #5	$149.53	6.753%	$159.6278	$159.63	$159.65	$159.60
Purchase #6	$162.28	6.484%	$172.8022	$172.80	$172.80	$172.80
Purchase #7	$176.27	10.570%	$194.9017	$194.90	$194.90	$194.90
7 purchase totals =	$1,008.72		$1,086.3937	$1,086.40	$1,086.40	$1,086.40