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	$16.57	7.780%	$17.8591	$17.86	$17.85	$17.90
Purchase #2	$232.29	13.827%	$264.4087	$264.41	$264.40	$264.40
Purchase #3	$30.37	10.321%	$33.5045	$33.50	$33.50	$33.50
Purchase #4	$58.91	11.187%	$65.5003	$65.50	$65.50	$65.50
Purchase #5	$115.58	8.233%	$125.0957	$125.10	$125.10	$125.10
Purchase #6	$109.43	12.863%	$123.506	$123.51	$123.50	$123.50
Purchase #7	$168.36	6.823%	$179.8472	$179.85	$179.85	$179.80
7 purchase totals =	$731.51		$809.7215	$809.73	$809.70	$809.70