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	$81.90	8.753%	$89.0687	$89.07	$89.05	$89.10
Purchase #2	$149.59	13.271%	$169.4421	$169.44	$169.45	$169.40
Purchase #3	$233.79	4.803%	$245.0189	$245.02	$245.00	$245.00
Purchase #4	$71.64	7.321%	$76.8848	$76.88	$76.90	$76.90
Purchase #5	$123.38	5.611%	$130.3029	$130.30	$130.30	$130.30
Purchase #6	$101.98	9.337%	$111.5019	$111.50	$111.50	$111.50
Purchase #7	$199.90	4.135%	$208.1659	$208.17	$208.15	$208.20
7 purchase totals =	$962.18		$1,030.3852	$1,030.38	$1,030.35	$1,030.40