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	$124.33	9.490%	$136.1289	$136.13	$136.15	$136.10
Purchase #2	$99.70	4.556%	$104.2423	$104.24	$104.25	$104.20
Purchase #3	$198.72	11.106%	$220.7898	$220.79	$220.80	$220.80
Purchase #4	$240.70	11.546%	$268.4912	$268.49	$268.50	$268.50
Purchase #5	$72.93	4.387%	$76.1294	$76.13	$76.15	$76.10
Purchase #6	$127.61	13.331%	$144.6217	$144.62	$144.60	$144.60
Purchase #7	$94.27	6.626%	$100.5163	$100.52	$100.50	$100.50
7 purchase totals =	$958.26		$1,050.9196	$1,050.92	$1,050.95	$1,050.80