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	$25.51	6.342%	$27.1278	$27.13	$27.15	$27.10
Purchase #2	$161.27	10.435%	$178.0985	$178.10	$178.10	$178.10
Purchase #3	$46.26	6.771%	$49.3923	$49.39	$49.40	$49.40
Purchase #4	$218.72	12.140%	$245.2726	$245.27	$245.25	$245.30
Purchase #5	$209.67	7.683%	$225.7789	$225.78	$225.80	$225.80
Purchase #6	$86.27	3.213%	$89.0419	$89.04	$89.05	$89.00
Purchase #7	$170.30	5.755%	$180.1008	$180.10	$180.10	$180.10
7 purchase totals =	$918.00		$994.8128	$994.81	$994.85	$994.80