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	$162.45	13.476%	$184.3418	$184.34	$184.35	$184.30
Purchase #2	$43.85	6.332%	$46.6266	$46.63	$46.65	$46.60
Purchase #3	$147.68	3.110%	$152.2728	$152.27	$152.25	$152.30
Purchase #4	$121.65	11.682%	$135.8612	$135.86	$135.85	$135.90
Purchase #5	$60.80	10.795%	$67.3634	$67.36	$67.35	$67.40
Purchase #6	$99.34	12.646%	$111.9025	$111.90	$111.90	$111.90
Purchase #7	$185.46	3.178%	$191.3539	$191.35	$191.35	$191.40
7 purchase totals =	$821.23		$889.7222	$889.71	$889.70	$889.80