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	$55.86	6.673%	$59.5875	$59.59	$59.60	$59.60
Purchase #2	$193.94	7.837%	$209.1391	$209.14	$209.15	$209.10
Purchase #3	$197.40	12.437%	$221.9506	$221.95	$221.95	$222.00
Purchase #4	$33.75	6.114%	$35.8135	$35.81	$35.80	$35.80
Purchase #5	$67.59	7.570%	$72.7066	$72.71	$72.70	$72.70
Purchase #6	$167.62	13.674%	$190.5404	$190.54	$190.55	$190.50
Purchase #7	$67.42	8.292%	$73.0105	$73.01	$73.00	$73.00
7 purchase totals =	$783.58		$862.7482	$862.75	$862.75	$862.70