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	$26.33	5.516%	$27.7824	$27.78	$27.80	$27.80
Purchase #2	$119.71	9.623%	$131.2297	$131.23	$131.25	$131.20
Purchase #3	$50.65	10.345%	$55.8897	$55.89	$55.90	$55.90
Purchase #4	$205.35	12.579%	$231.181	$231.18	$231.20	$231.20
Purchase #5	$233.40	13.455%	$264.804	$264.80	$264.80	$264.80
Purchase #6	$20.54	5.356%	$21.6401	$21.64	$21.65	$21.60
Purchase #7	$164.56	11.467%	$183.4301	$183.43	$183.45	$183.40
7 purchase totals =	$820.54		$915.9570	$915.95	$916.05	$915.90