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	$101.26	5.467%	$106.7959	$106.80	$106.80	$106.80
Purchase #2	$64.60	10.794%	$71.5729	$71.57	$71.55	$71.60
Purchase #3	$142.76	11.734%	$159.5115	$159.51	$159.50	$159.50
Purchase #4	$191.92	12.173%	$215.2824	$215.28	$215.30	$215.30
Purchase #5	$92.69	10.487%	$102.4104	$102.41	$102.40	$102.40
Purchase #6	$58.77	11.520%	$65.5403	$65.54	$65.55	$65.50
Purchase #7	$42.44	6.340%	$45.1307	$45.13	$45.15	$45.10
7 purchase totals =	$694.44		$766.2441	$766.24	$766.25	$766.20