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	$51.72	10.242%	$57.0172	$57.02	$57.00	$57.00
Purchase #2	$118.53	9.209%	$129.4454	$129.45	$129.45	$129.40
Purchase #3	$120.74	8.652%	$131.1864	$131.19	$131.20	$131.20
Purchase #4	$91.27	9.419%	$99.8667	$99.87	$99.85	$99.90
Purchase #5	$65.97	8.364%	$71.4877	$71.49	$71.50	$71.50
Purchase #6	$179.58	3.134%	$185.208	$185.21	$185.20	$185.20
Purchase #7	$41.82	10.863%	$46.3629	$46.36	$46.35	$46.40
7 purchase totals =	$669.63		$720.5743	$720.59	$720.55	$720.60