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	$233.85	8.351%	$253.3788	$253.38	$253.40	$253.40
Purchase #2	$248.75	8.193%	$269.1301	$269.13	$269.15	$269.10
Purchase #3	$67.53	5.114%	$70.9835	$70.98	$71.00	$71.00
Purchase #4	$18.25	3.839%	$18.9506	$18.95	$18.95	$19.00
Purchase #5	$99.74	10.132%	$109.8457	$109.85	$109.85	$109.80
Purchase #6	$86.90	13.600%	$98.7184	$98.72	$98.70	$98.70
Purchase #7	$16.76	10.406%	$18.504	$18.50	$18.50	$18.50
7 purchase totals =	$771.78		$839.5111	$839.51	$839.55	$839.50