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	$138.72	11.362%	$154.4814	$154.48	$154.50	$154.50
Purchase #2	$249.48	10.434%	$275.5107	$275.51	$275.50	$275.50
Purchase #3	$135.37	3.827%	$140.5506	$140.55	$140.55	$140.60
Purchase #4	$80.65	13.396%	$91.4539	$91.45	$91.45	$91.50
Purchase #5	$32.89	6.568%	$35.0502	$35.05	$35.05	$35.10
Purchase #6	$68.90	10.835%	$76.3653	$76.37	$76.35	$76.40
Purchase #7	$247.93	3.317%	$256.1538	$256.15	$256.15	$256.20
7 purchase totals =	$953.94		$1,029.5659	$1,029.56	$1,029.55	$1,029.80