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	$20.47	6.557%	$21.8122	$21.81	$21.80	$21.80
Purchase #2	$70.60	4.512%	$73.7855	$73.79	$73.80	$73.80
Purchase #3	$206.34	9.739%	$226.4355	$226.44	$226.45	$226.40
Purchase #4	$59.74	12.624%	$67.2816	$67.28	$67.30	$67.30
Purchase #5	$147.88	5.303%	$155.7221	$155.72	$155.70	$155.70
Purchase #6	$241.93	9.369%	$264.5964	$264.60	$264.60	$264.60
Purchase #7	$79.59	12.342%	$89.413	$89.41	$89.40	$89.40
7 purchase totals =	$826.55		$899.0463	$899.05	$899.05	$899.00