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	$66.40	8.162%	$71.8196	$71.82	$71.80	$71.80
Purchase #2	$181.77	4.739%	$190.3841	$190.38	$190.40	$190.40
Purchase #3	$140.72	5.841%	$148.9395	$148.94	$148.95	$148.90
Purchase #4	$25.72	8.689%	$27.9548	$27.95	$27.95	$28.00
Purchase #5	$63.76	6.437%	$67.8642	$67.86	$67.85	$67.90
Purchase #6	$182.43	11.833%	$204.0169	$204.02	$204.00	$204.00
Purchase #7	$99.55	4.834%	$104.3622	$104.36	$104.35	$104.40
7 purchase totals =	$760.35		$815.3413	$815.33	$815.30	$815.40