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	$55.36	10.274%	$61.0477	$61.05	$61.05	$61.00
Purchase #2	$20.41	5.751%	$21.5838	$21.58	$21.60	$21.60
Purchase #3	$96.74	4.226%	$100.8282	$100.83	$100.85	$100.80
Purchase #4	$133.69	4.392%	$139.5617	$139.56	$139.55	$139.60
Purchase #5	$177.69	3.319%	$183.5875	$183.59	$183.60	$183.60
Purchase #6	$196.36	12.640%	$221.1799	$221.18	$221.20	$221.20
Purchase #7	$94.35	4.788%	$98.8675	$98.87	$98.85	$98.90
7 purchase totals =	$774.60		$826.6563	$826.66	$826.70	$826.70