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	$160.66	3.482%	$166.2542	$166.25	$166.25	$166.30
Purchase #2	$188.27	12.644%	$212.0749	$212.07	$212.05	$212.10
Purchase #3	$167.44	3.238%	$172.8617	$172.86	$172.85	$172.90
Purchase #4	$250.34	11.577%	$279.3219	$279.32	$279.30	$279.30
Purchase #5	$89.93	6.680%	$95.9373	$95.94	$95.95	$95.90
Purchase #6	$27.59	4.834%	$28.9237	$28.92	$28.90	$28.90
Purchase #7	$195.46	12.244%	$219.3921	$219.39	$219.40	$219.40
7 purchase totals =	$1,079.69		$1,174.7658	$1,174.75	$1,174.70	$1,174.80