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	$87.96	12.533%	$98.984	$98.98	$99.00	$99.00
Purchase #2	$103.99	4.530%	$108.7007	$108.70	$108.70	$108.70
Purchase #3	$70.84	10.299%	$78.1358	$78.14	$78.15	$78.10
Purchase #4	$68.84	12.285%	$77.297	$77.30	$77.30	$77.30
Purchase #5	$70.99	11.700%	$79.2958	$79.30	$79.30	$79.30
Purchase #6	$104.98	6.483%	$111.7859	$111.79	$111.80	$111.80
Purchase #7	$32.81	13.154%	$37.1258	$37.13	$37.15	$37.10
7 purchase totals =	$540.41		$591.3250	$591.34	$591.40	$591.30