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	$101.98	4.210%	$106.2734	$106.27	$106.25	$106.30
Purchase #2	$78.37	9.801%	$86.051	$86.05	$86.05	$86.10
Purchase #3	$67.38	12.405%	$75.7385	$75.74	$75.75	$75.70
Purchase #4	$26.63	9.260%	$29.0959	$29.10	$29.10	$29.10
Purchase #5	$139.51	6.308%	$148.3103	$148.31	$148.30	$148.30
Purchase #6	$64.98	4.444%	$67.8677	$67.87	$67.85	$67.90
Purchase #7	$42.78	6.535%	$45.5757	$45.58	$45.60	$45.60
7 purchase totals =	$521.63		$558.9125	$558.92	$558.90	$559.00