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	$73.42	7.409%	$78.8597	$78.86	$78.85	$78.90
Purchase #2	$96.58	9.340%	$105.6006	$105.60	$105.60	$105.60
Purchase #3	$136.96	13.573%	$155.5496	$155.55	$155.55	$155.50
Purchase #4	$211.62	8.464%	$229.5315	$229.53	$229.55	$229.50
Purchase #5	$14.66	4.469%	$15.3152	$15.32	$15.30	$15.30
Purchase #6	$193.73	13.516%	$219.9145	$219.91	$219.90	$219.90
Purchase #7	$93.68	8.221%	$101.3814	$101.38	$101.40	$101.40
7 purchase totals =	$820.65		$906.1525	$906.15	$906.15	$906.10