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	$35.89	13.798%	$40.8421	$40.84	$40.85	$40.80
Purchase #2	$122.70	10.866%	$136.0326	$136.03	$136.05	$136.00
Purchase #3	$199.91	4.795%	$209.4957	$209.50	$209.50	$209.50
Purchase #4	$240.35	13.600%	$273.0376	$273.04	$273.05	$273.00
Purchase #5	$45.85	10.866%	$50.8321	$50.83	$50.85	$50.80
Purchase #6	$27.64	13.646%	$31.4118	$31.41	$31.40	$31.40
Purchase #7	$240.61	11.570%	$268.4486	$268.45	$268.45	$268.40
7 purchase totals =	$912.95		$1,010.1005	$1,010.10	$1,010.15	$1,009.90