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	$74.35	12.105%	$83.3501	$83.35	$83.35	$83.40
Purchase #2	$142.65	13.324%	$161.6567	$161.66	$161.65	$161.70
Purchase #3	$174.44	6.615%	$185.9792	$185.98	$186.00	$186.00
Purchase #4	$34.46	7.827%	$37.1572	$37.16	$37.15	$37.20
Purchase #5	$33.72	9.196%	$36.8209	$36.82	$36.80	$36.80
Purchase #6	$85.46	8.661%	$92.8617	$92.86	$92.85	$92.90
Purchase #7	$148.61	13.310%	$168.39	$168.39	$168.40	$168.40
7 purchase totals =	$693.69		$766.2158	$766.22	$766.20	$766.40