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	$52.96	12.707%	$59.6896	$59.69	$59.70	$59.70
Purchase #2	$217.66	12.225%	$244.2689	$244.27	$244.25	$244.30
Purchase #3	$180.49	6.332%	$191.9186	$191.92	$191.90	$191.90
Purchase #4	$85.57	13.113%	$96.7908	$96.79	$96.80	$96.80
Purchase #5	$128.42	7.413%	$137.9398	$137.94	$137.95	$137.90
Purchase #6	$239.90	12.607%	$270.1442	$270.14	$270.15	$270.10
Purchase #7	$91.30	5.174%	$96.0239	$96.02	$96.00	$96.00
7 purchase totals =	$996.30		$1,096.7758	$1,096.77	$1,096.75	$1,096.70