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	$94.50	6.642%	$100.7767	$100.78	$100.80	$100.80
Purchase #2	$85.95	4.826%	$90.0979	$90.10	$90.10	$90.10
Purchase #3	$101.76	5.243%	$107.0953	$107.10	$107.10	$107.10
Purchase #4	$240.44	10.154%	$264.8543	$264.85	$264.85	$264.90
Purchase #5	$65.60	8.336%	$71.0684	$71.07	$71.05	$71.10
Purchase #6	$213.33	3.776%	$221.3853	$221.39	$221.40	$221.40
Purchase #7	$31.99	3.840%	$33.2184	$33.22	$33.20	$33.20
7 purchase totals =	$833.57		$888.4963	$888.51	$888.50	$888.60