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	$230.92	4.172%	$240.554	$240.55	$240.55	$240.60
Purchase #2	$183.93	6.790%	$196.4188	$196.42	$196.40	$196.40
Purchase #3	$79.79	4.179%	$83.1244	$83.12	$83.10	$83.10
Purchase #4	$149.33	7.656%	$160.7627	$160.76	$160.75	$160.80
Purchase #5	$78.59	13.334%	$89.0692	$89.07	$89.05	$89.10
Purchase #6	$215.77	7.123%	$231.1393	$231.14	$231.15	$231.10
Purchase #7	$51.86	6.408%	$55.1832	$55.18	$55.20	$55.20
7 purchase totals =	$990.19		$1,056.2516	$1,056.24	$1,056.20	$1,056.30