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	$87.74	13.603%	$99.6753	$99.68	$99.70	$99.70
Purchase #2	$196.39	12.418%	$220.7777	$220.78	$220.80	$220.80
Purchase #3	$136.86	13.370%	$155.1582	$155.16	$155.15	$155.20
Purchase #4	$50.37	5.753%	$53.2678	$53.27	$53.25	$53.30
Purchase #5	$190.28	10.340%	$209.955	$209.96	$209.95	$210.00
Purchase #6	$156.67	7.807%	$168.9012	$168.90	$168.90	$168.90
Purchase #7	$147.57	12.684%	$166.2878	$166.29	$166.30	$166.30
7 purchase totals =	$965.88		$1,074.0230	$1,074.04	$1,074.05	$1,074.20