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	$129.84	9.756%	$142.5072	$142.51	$142.50	$142.50
Purchase #2	$166.68	13.487%	$189.1601	$189.16	$189.15	$189.20
Purchase #3	$142.86	6.508%	$152.1573	$152.16	$152.15	$152.20
Purchase #4	$102.61	7.221%	$110.0195	$110.02	$110.00	$110.00
Purchase #5	$158.64	4.747%	$166.1706	$166.17	$166.15	$166.20
Purchase #6	$46.86	11.537%	$52.2662	$52.27	$52.25	$52.30
Purchase #7	$212.65	3.115%	$219.274	$219.27	$219.25	$219.30
7 purchase totals =	$960.14		$1,031.5549	$1,031.56	$1,031.45	$1,031.70