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	$88.43	13.801%	$100.6342	$100.63	$100.65	$100.60
Purchase #2	$209.87	9.759%	$230.3512	$230.35	$230.35	$230.40
Purchase #3	$85.59	8.834%	$93.151	$93.15	$93.15	$93.20
Purchase #4	$142.48	5.788%	$150.7267	$150.73	$150.75	$150.70
Purchase #5	$72.93	10.818%	$80.8196	$80.82	$80.80	$80.80
Purchase #6	$172.90	10.527%	$191.1012	$191.10	$191.10	$191.10
Purchase #7	$232.96	4.593%	$243.6599	$243.66	$243.65	$243.70
7 purchase totals =	$1,005.16		$1,090.4438	$1,090.44	$1,090.45	$1,090.50