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	$156.84	7.128%	$168.0196	$168.02	$168.00	$168.00
Purchase #2	$78.59	9.819%	$86.3068	$86.31	$86.30	$86.30
Purchase #3	$72.50	10.559%	$80.1553	$80.16	$80.15	$80.20
Purchase #4	$238.25	4.701%	$249.4501	$249.45	$249.45	$249.50
Purchase #5	$138.55	9.869%	$152.2235	$152.22	$152.20	$152.20
Purchase #6	$152.27	3.233%	$157.1929	$157.19	$157.20	$157.20
Purchase #7	$173.39	11.563%	$193.4391	$193.44	$193.45	$193.40
7 purchase totals =	$1,010.39		$1,086.7873	$1,086.79	$1,086.75	$1,086.80