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	$80.81	13.305%	$91.5618	$91.56	$91.55	$91.60
Purchase #2	$94.73	8.796%	$103.0625	$103.06	$103.05	$103.10
Purchase #3	$236.96	10.816%	$262.5896	$262.59	$262.60	$262.60
Purchase #4	$79.76	7.577%	$85.8034	$85.80	$85.80	$85.80
Purchase #5	$51.49	8.532%	$55.8831	$55.88	$55.90	$55.90
Purchase #6	$218.40	11.555%	$243.6361	$243.64	$243.65	$243.60
Purchase #7	$9.71	9.190%	$10.6023	$10.60	$10.60	$10.60
7 purchase totals =	$771.86		$853.1388	$853.13	$853.15	$853.20