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	$169.31	11.336%	$188.503	$188.50	$188.50	$188.50
Purchase #2	$55.74	13.617%	$63.3301	$63.33	$63.35	$63.30
Purchase #3	$226.72	10.616%	$250.7886	$250.79	$250.80	$250.80
Purchase #4	$30.39	10.558%	$33.5986	$33.60	$33.60	$33.60
Purchase #5	$40.56	9.791%	$44.5312	$44.53	$44.55	$44.50
Purchase #6	$226.96	5.395%	$239.2045	$239.20	$239.20	$239.20
Purchase #7	$107.73	3.563%	$111.5684	$111.57	$111.55	$111.60
7 purchase totals =	$857.41		$931.5244	$931.52	$931.55	$931.50