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	$166.34	9.698%	$182.4717	$182.47	$182.45	$182.50
Purchase #2	$58.77	7.717%	$63.3053	$63.31	$63.30	$63.30
Purchase #3	$199.93	11.426%	$222.774	$222.77	$222.75	$222.80
Purchase #4	$96.48	4.625%	$100.9422	$100.94	$100.95	$100.90
Purchase #5	$83.31	6.554%	$88.7701	$88.77	$88.75	$88.80
Purchase #6	$162.78	4.796%	$170.5869	$170.59	$170.60	$170.60
Purchase #7	$6.50	7.616%	$6.995	$7.00	$7.00	$7.00
7 purchase totals =	$774.11		$835.8452	$835.85	$835.80	$835.90