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	$156.40	11.111%	$173.7776	$173.78	$173.80	$173.80
Purchase #2	$106.59	10.494%	$117.7756	$117.78	$117.80	$117.80
Purchase #3	$79.87	13.627%	$90.7539	$90.75	$90.75	$90.80
Purchase #4	$92.28	9.394%	$100.9488	$100.95	$100.95	$100.90
Purchase #5	$17.94	5.695%	$18.9617	$18.96	$18.95	$19.00
Purchase #6	$89.59	7.515%	$96.3227	$96.32	$96.30	$96.30
Purchase #7	$242.96	6.505%	$258.7645	$258.76	$258.75	$258.80
7 purchase totals =	$785.63		$857.3048	$857.30	$857.30	$857.40