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	$206.95	5.701%	$218.7482	$218.75	$218.75	$218.70
Purchase #2	$65.93	9.645%	$72.2889	$72.29	$72.30	$72.30
Purchase #3	$52.41	5.427%	$55.2543	$55.25	$55.25	$55.30
Purchase #4	$80.39	6.816%	$85.8694	$85.87	$85.85	$85.90
Purchase #5	$49.80	11.589%	$55.5713	$55.57	$55.55	$55.60
Purchase #6	$140.99	3.440%	$145.8401	$145.84	$145.85	$145.80
Purchase #7	$39.70	12.316%	$44.5895	$44.59	$44.60	$44.60
7 purchase totals =	$636.17		$678.1617	$678.16	$678.15	$678.20