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	$147.31	13.608%	$167.3559	$167.36	$167.35	$167.40
Purchase #2	$164.92	7.200%	$176.7942	$176.79	$176.80	$176.80
Purchase #3	$77.85	9.690%	$85.3937	$85.39	$85.40	$85.40
Purchase #4	$243.72	13.157%	$275.7862	$275.79	$275.80	$275.80
Purchase #5	$107.82	7.689%	$116.1103	$116.11	$116.10	$116.10
Purchase #6	$82.25	7.457%	$88.3834	$88.38	$88.40	$88.40
Purchase #7	$163.83	4.532%	$171.2548	$171.25	$171.25	$171.30
7 purchase totals =	$987.70		$1,081.0785	$1,081.07	$1,081.10	$1,081.20