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	$40.33	6.204%	$42.8321	$42.83	$42.85	$42.80
Purchase #2	$69.80	9.362%	$76.3347	$76.33	$76.35	$76.30
Purchase #3	$233.88	4.107%	$243.4855	$243.49	$243.50	$243.50
Purchase #4	$200.32	8.118%	$216.582	$216.58	$216.60	$216.60
Purchase #5	$145.62	10.178%	$160.4412	$160.44	$160.45	$160.40
Purchase #6	$116.35	9.449%	$127.3439	$127.34	$127.35	$127.30
Purchase #7	$120.53	4.491%	$125.943	$125.94	$125.95	$125.90
7 purchase totals =	$926.83		$992.9624	$992.95	$993.05	$992.80