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	$35.75	13.489%	$40.5723	$40.57	$40.55	$40.60
Purchase #2	$186.28	3.769%	$193.3009	$193.30	$193.30	$193.30
Purchase #3	$184.73	13.685%	$210.0103	$210.01	$210.00	$210.00
Purchase #4	$250.49	7.766%	$269.9431	$269.94	$269.95	$269.90
Purchase #5	$196.51	13.700%	$223.4319	$223.43	$223.45	$223.40
Purchase #6	$136.79	10.783%	$151.5401	$151.54	$151.55	$151.50
Purchase #7	$240.80	12.826%	$271.685	$271.69	$271.70	$271.70
7 purchase totals =	$1,231.35		$1,360.4836	$1,360.48	$1,360.50	$1,360.40