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	$50.29	13.265%	$56.961	$56.96	$56.95	$57.00
Purchase #2	$71.96	9.401%	$78.725	$78.73	$78.75	$78.70
Purchase #3	$141.52	8.679%	$153.8025	$153.80	$153.80	$153.80
Purchase #4	$96.80	8.818%	$105.3358	$105.34	$105.35	$105.30
Purchase #5	$167.68	10.615%	$185.4792	$185.48	$185.50	$185.50
Purchase #6	$106.61	7.529%	$114.6367	$114.64	$114.65	$114.60
Purchase #7	$237.48	4.813%	$248.9099	$248.91	$248.90	$248.90
7 purchase totals =	$872.34		$943.8501	$943.86	$943.90	$943.80