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	$178.84	3.334%	$184.8025	$184.80	$184.80	$184.80
Purchase #2	$169.82	11.121%	$188.7057	$188.71	$188.70	$188.70
Purchase #3	$221.92	4.501%	$231.9086	$231.91	$231.90	$231.90
Purchase #4	$73.62	11.731%	$82.2564	$82.26	$82.25	$82.30
Purchase #5	$139.59	3.362%	$144.283	$144.28	$144.30	$144.30
Purchase #6	$43.57	7.599%	$46.8809	$46.88	$46.90	$46.90
Purchase #7	$228.54	9.288%	$249.7668	$249.77	$249.75	$249.80
7 purchase totals =	$1,055.90		$1,128.6039	$1,128.61	$1,128.60	$1,128.70