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	$82.69	9.150%	$90.2561	$90.26	$90.25	$90.30
Purchase #2	$62.96	9.297%	$68.8134	$68.81	$68.80	$68.80
Purchase #3	$68.79	10.282%	$75.863	$75.86	$75.85	$75.90
Purchase #4	$190.33	9.178%	$207.7985	$207.80	$207.80	$207.80
Purchase #5	$192.46	9.782%	$211.2864	$211.29	$211.30	$211.30
Purchase #6	$153.79	12.148%	$172.4724	$172.47	$172.45	$172.50
Purchase #7	$139.59	9.117%	$152.3164	$152.32	$152.30	$152.30
7 purchase totals =	$890.61		$978.8062	$978.81	$978.75	$978.90