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	$96.98	3.629%	$100.4994	$100.50	$100.50	$100.50
Purchase #2	$19.27	9.146%	$21.0324	$21.03	$21.05	$21.00
Purchase #3	$204.26	11.270%	$227.2801	$227.28	$227.30	$227.30
Purchase #4	$221.59	8.673%	$240.8085	$240.81	$240.80	$240.80
Purchase #5	$59.30	4.869%	$62.1873	$62.19	$62.20	$62.20
Purchase #6	$80.91	5.140%	$85.0688	$85.07	$85.05	$85.10
Purchase #7	$46.94	7.676%	$50.5431	$50.54	$50.55	$50.50
7 purchase totals =	$729.25		$787.4196	$787.42	$787.45	$787.40