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	$86.51	6.164%	$91.8425	$91.84	$91.85	$91.80
Purchase #2	$72.60	5.794%	$76.8064	$76.81	$76.80	$76.80
Purchase #3	$128.83	9.105%	$140.56	$140.56	$140.55	$140.60
Purchase #4	$112.81	4.163%	$117.5063	$117.51	$117.50	$117.50
Purchase #5	$51.52	5.220%	$54.2093	$54.21	$54.20	$54.20
Purchase #6	$28.53	11.279%	$31.7479	$31.75	$31.75	$31.70
Purchase #7	$243.99	8.111%	$263.78	$263.78	$263.80	$263.80
7 purchase totals =	$724.79		$776.4524	$776.46	$776.45	$776.40