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	$111.79	10.779%	$123.8398	$123.84	$123.85	$123.80
Purchase #2	$56.56	5.158%	$59.4774	$59.48	$59.50	$59.50
Purchase #3	$88.44	5.466%	$93.2741	$93.27	$93.25	$93.30
Purchase #4	$246.62	10.709%	$273.0305	$273.03	$273.05	$273.00
Purchase #5	$185.47	4.561%	$193.9293	$193.93	$193.95	$193.90
Purchase #6	$37.39	12.313%	$41.9938	$41.99	$42.00	$42.00
Purchase #7	$197.50	4.275%	$205.9431	$205.94	$205.95	$205.90
7 purchase totals =	$923.77		$991.4880	$991.48	$991.55	$991.40