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	$160.91	6.371%	$171.1616	$171.16	$171.15	$171.20
Purchase #2	$46.59	3.431%	$48.1885	$48.19	$48.20	$48.20
Purchase #3	$233.41	13.124%	$264.0427	$264.04	$264.05	$264.00
Purchase #4	$117.88	11.512%	$131.4503	$131.45	$131.45	$131.50
Purchase #5	$18.71	6.685%	$19.9608	$19.96	$19.95	$20.00
Purchase #6	$168.97	6.689%	$180.2724	$180.27	$180.25	$180.30
Purchase #7	$230.28	8.590%	$250.0611	$250.06	$250.05	$250.10
7 purchase totals =	$976.75		$1,065.1374	$1,065.13	$1,065.10	$1,065.30