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	$145.46	6.792%	$155.3396	$155.34	$155.35	$155.30
Purchase #2	$104.66	11.349%	$116.5379	$116.54	$116.55	$116.50
Purchase #3	$119.63	11.197%	$133.025	$133.03	$133.05	$133.00
Purchase #4	$152.75	6.224%	$162.2572	$162.26	$162.25	$162.30
Purchase #5	$144.69	5.133%	$152.1169	$152.12	$152.10	$152.10
Purchase #6	$31.59	9.188%	$34.4925	$34.49	$34.50	$34.50
Purchase #7	$71.48	12.440%	$80.3721	$80.37	$80.35	$80.40
7 purchase totals =	$770.26		$834.1412	$834.15	$834.15	$834.10