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	$171.51	6.343%	$182.3889	$182.39	$182.40	$182.40
Purchase #2	$148.55	9.431%	$162.5598	$162.56	$162.55	$162.60
Purchase #3	$165.60	12.105%	$185.6459	$185.65	$185.65	$185.60
Purchase #4	$31.45	5.760%	$33.2615	$33.26	$33.25	$33.30
Purchase #5	$233.25	7.230%	$250.114	$250.11	$250.10	$250.10
Purchase #6	$7.79	6.570%	$8.3018	$8.30	$8.30	$8.30
Purchase #7	$91.88	11.269%	$102.234	$102.23	$102.25	$102.20
7 purchase totals =	$850.03		$924.5059	$924.50	$924.50	$924.50