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	$43.26	4.666%	$45.2785	$45.28	$45.30	$45.30
Purchase #2	$150.66	6.325%	$160.1892	$160.19	$160.20	$160.20
Purchase #3	$154.60	10.790%	$171.2813	$171.28	$171.30	$171.30
Purchase #4	$35.78	6.129%	$37.973	$37.97	$37.95	$38.00
Purchase #5	$70.52	10.838%	$78.163	$78.16	$78.15	$78.20
Purchase #6	$157.53	3.164%	$162.5142	$162.51	$162.50	$162.50
Purchase #7	$229.96	5.407%	$242.3939	$242.39	$242.40	$242.40
7 purchase totals =	$842.31		$897.7931	$897.78	$897.80	$897.90