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	$15.38	7.207%	$16.4884	$16.49	$16.50	$16.50
Purchase #2	$162.93	3.287%	$168.2855	$168.29	$168.30	$168.30
Purchase #3	$205.80	12.341%	$231.1978	$231.20	$231.20	$231.20
Purchase #4	$84.61	5.608%	$89.3549	$89.35	$89.35	$89.40
Purchase #5	$86.34	5.846%	$91.3874	$91.39	$91.40	$91.40
Purchase #6	$233.83	9.743%	$256.6121	$256.61	$256.60	$256.60
Purchase #7	$141.89	3.642%	$147.0576	$147.06	$147.05	$147.10
7 purchase totals =	$930.78		$1,000.3837	$1,000.39	$1,000.40	$1,000.50