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	$229.26	12.578%	$258.0963	$258.10	$258.10	$258.10
Purchase #2	$178.31	10.190%	$196.4798	$196.48	$196.50	$196.50
Purchase #3	$141.37	7.677%	$152.223	$152.22	$152.20	$152.20
Purchase #4	$45.25	9.432%	$49.518	$49.52	$49.50	$49.50
Purchase #5	$92.71	3.365%	$95.8297	$95.83	$95.85	$95.80
Purchase #6	$89.89	7.618%	$96.7378	$96.74	$96.75	$96.70
Purchase #7	$21.61	6.431%	$22.9997	$23.00	$23.00	$23.00
7 purchase totals =	$798.40		$871.8843	$871.89	$871.90	$871.80