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	$227.63	10.250%	$250.9621	$250.96	$250.95	$251.00
Purchase #2	$79.85	12.472%	$89.8089	$89.81	$89.80	$89.80
Purchase #3	$89.39	13.782%	$101.7097	$101.71	$101.70	$101.70
Purchase #4	$220.60	12.156%	$247.4161	$247.42	$247.40	$247.40
Purchase #5	$104.72	7.489%	$112.5625	$112.56	$112.55	$112.60
Purchase #6	$64.84	8.648%	$70.4474	$70.45	$70.45	$70.40
Purchase #7	$228.58	7.555%	$245.8492	$245.85	$245.85	$245.80
7 purchase totals =	$1,015.61		$1,118.7559	$1,118.76	$1,118.70	$1,118.70