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	$192.60	9.700%	$211.2822	$211.28	$211.30	$211.30
Purchase #2	$161.71	10.739%	$179.076	$179.08	$179.10	$179.10
Purchase #3	$131.89	5.674%	$139.3734	$139.37	$139.35	$139.40
Purchase #4	$43.84	7.510%	$47.1324	$47.13	$47.15	$47.10
Purchase #5	$198.83	13.242%	$225.1591	$225.16	$225.15	$225.20
Purchase #6	$52.90	5.528%	$55.8243	$55.82	$55.80	$55.80
Purchase #7	$69.57	11.484%	$77.5594	$77.56	$77.55	$77.60
7 purchase totals =	$851.34		$935.4068	$935.40	$935.40	$935.50