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	$202.62	13.459%	$229.8906	$229.89	$229.90	$229.90
Purchase #2	$94.78	6.117%	$100.5777	$100.58	$100.60	$100.60
Purchase #3	$242.36	12.707%	$273.1567	$273.16	$273.15	$273.20
Purchase #4	$80.81	12.173%	$90.647	$90.65	$90.65	$90.60
Purchase #5	$180.98	12.134%	$202.9401	$202.94	$202.95	$202.90
Purchase #6	$121.32	4.373%	$126.6253	$126.63	$126.65	$126.60
Purchase #7	$68.92	11.383%	$76.7652	$76.77	$76.75	$76.80
7 purchase totals =	$991.79		$1,100.6026	$1,100.62	$1,100.65	$1,100.60