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	$91.94	13.646%	$104.4861	$104.49	$104.50	$104.50
Purchase #2	$239.83	13.224%	$271.5451	$271.55	$271.55	$271.50
Purchase #3	$65.79	9.296%	$71.9058	$71.91	$71.90	$71.90
Purchase #4	$66.64	7.480%	$71.6247	$71.62	$71.60	$71.60
Purchase #5	$145.62	11.742%	$162.7187	$162.72	$162.70	$162.70
Purchase #6	$62.65	8.285%	$67.8406	$67.84	$67.85	$67.80
Purchase #7	$94.35	12.671%	$106.3051	$106.31	$106.30	$106.30
7 purchase totals =	$766.82		$856.4261	$856.44	$856.40	$856.30