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	$142.28	3.672%	$147.5045	$147.50	$147.50	$147.50
Purchase #2	$249.41	9.251%	$272.4829	$272.48	$272.50	$272.50
Purchase #3	$67.82	6.630%	$72.3165	$72.32	$72.30	$72.30
Purchase #4	$37.91	8.517%	$41.1388	$41.14	$41.15	$41.10
Purchase #5	$216.89	10.275%	$239.1754	$239.18	$239.20	$239.20
Purchase #6	$134.84	9.409%	$147.5271	$147.53	$147.55	$147.50
Purchase #7	$142.33	11.441%	$158.614	$158.61	$158.60	$158.60
7 purchase totals =	$991.48		$1,078.7592	$1,078.76	$1,078.80	$1,078.70