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	$5.65	10.259%	$6.2296	$6.23	$6.25	$6.20
Purchase #2	$51.92	4.237%	$54.1199	$54.12	$54.10	$54.10
Purchase #3	$143.62	6.248%	$152.5934	$152.59	$152.60	$152.60
Purchase #4	$31.81	4.188%	$33.1422	$33.14	$33.15	$33.10
Purchase #5	$160.34	9.339%	$175.3142	$175.31	$175.30	$175.30
Purchase #6	$201.41	6.131%	$213.7584	$213.76	$213.75	$213.80
Purchase #7	$184.75	13.342%	$209.3993	$209.40	$209.40	$209.40
7 purchase totals =	$779.50		$844.5570	$844.55	$844.55	$844.50