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	$68.59	13.787%	$78.0465	$78.05	$78.05	$78.00
Purchase #2	$216.86	4.608%	$226.8529	$226.85	$226.85	$226.90
Purchase #3	$159.92	7.830%	$172.4417	$172.44	$172.45	$172.40
Purchase #4	$116.64	12.463%	$131.1768	$131.18	$131.20	$131.20
Purchase #5	$148.38	13.781%	$168.8282	$168.83	$168.85	$168.80
Purchase #6	$43.41	13.478%	$49.2608	$49.26	$49.25	$49.30
Purchase #7	$166.33	6.645%	$177.3826	$177.38	$177.40	$177.40
7 purchase totals =	$920.13		$1,003.9895	$1,003.99	$1,004.05	$1,004.00