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	$91.25	11.524%	$101.7657	$101.77	$101.75	$101.80
Purchase #2	$158.28	6.326%	$168.2928	$168.29	$168.30	$168.30
Purchase #3	$72.48	11.514%	$80.8253	$80.83	$80.85	$80.80
Purchase #4	$162.26	11.487%	$180.8988	$180.90	$180.90	$180.90
Purchase #5	$25.86	6.135%	$27.4465	$27.45	$27.45	$27.40
Purchase #6	$133.59	8.236%	$144.5925	$144.59	$144.60	$144.60
Purchase #7	$159.75	9.152%	$174.3703	$174.37	$174.35	$174.40
7 purchase totals =	$803.47		$878.1919	$878.20	$878.20	$878.20