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	$120.36	12.163%	$134.9994	$135.00	$135.00	$135.00
Purchase #2	$136.33	11.810%	$152.4306	$152.43	$152.45	$152.40
Purchase #3	$109.48	12.843%	$123.5405	$123.54	$123.55	$123.50
Purchase #4	$11.28	11.494%	$12.5765	$12.58	$12.60	$12.60
Purchase #5	$95.66	3.846%	$99.3391	$99.34	$99.35	$99.30
Purchase #6	$186.57	13.798%	$212.3129	$212.31	$212.30	$212.30
Purchase #7	$52.41	4.804%	$54.9278	$54.93	$54.95	$54.90
7 purchase totals =	$712.09		$790.1268	$790.13	$790.20	$790.00