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	$234.73	3.649%	$243.2953	$243.30	$243.30	$243.30
Purchase #2	$61.41	6.412%	$65.3476	$65.35	$65.35	$65.30
Purchase #3	$107.61	7.422%	$115.5968	$115.60	$115.60	$115.60
Purchase #4	$148.99	7.105%	$159.5757	$159.58	$159.60	$159.60
Purchase #5	$234.58	12.667%	$264.2942	$264.29	$264.30	$264.30
Purchase #6	$31.59	4.112%	$32.889	$32.89	$32.90	$32.90
Purchase #7	$159.94	9.121%	$174.5281	$174.53	$174.55	$174.50
7 purchase totals =	$978.85		$1,055.5267	$1,055.54	$1,055.60	$1,055.50