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	$73.42	6.819%	$78.4265	$78.43	$78.45	$78.40
Purchase #2	$184.29	6.388%	$196.0624	$196.06	$196.05	$196.10
Purchase #3	$233.78	11.835%	$261.4479	$261.45	$261.45	$261.40
Purchase #4	$188.40	8.151%	$203.7565	$203.76	$203.75	$203.80
Purchase #5	$182.26	11.566%	$203.3402	$203.34	$203.35	$203.30
Purchase #6	$34.63	9.543%	$37.9347	$37.93	$37.95	$37.90
Purchase #7	$72.46	4.350%	$75.612	$75.61	$75.60	$75.60
7 purchase totals =	$969.24		$1,056.5802	$1,056.58	$1,056.60	$1,056.50