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	$90.74	10.766%	$100.5091	$100.51	$100.50	$100.50
Purchase #2	$38.98	6.212%	$41.4014	$41.40	$41.40	$41.40
Purchase #3	$20.67	3.256%	$21.343	$21.34	$21.35	$21.30
Purchase #4	$188.76	11.476%	$210.4221	$210.42	$210.40	$210.40
Purchase #5	$249.64	5.373%	$263.0532	$263.05	$263.05	$263.10
Purchase #6	$242.90	3.496%	$251.3918	$251.39	$251.40	$251.40
Purchase #7	$147.60	3.537%	$152.8206	$152.82	$152.80	$152.80
7 purchase totals =	$979.29		$1,040.9412	$1,040.93	$1,040.90	$1,040.90