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	$63.56	11.334%	$70.7639	$70.76	$70.75	$70.80
Purchase #2	$140.80	3.218%	$145.3309	$145.33	$145.35	$145.30
Purchase #3	$65.54	7.414%	$70.3991	$70.40	$70.40	$70.40
Purchase #4	$215.50	12.542%	$242.528	$242.53	$242.55	$242.50
Purchase #5	$69.32	13.644%	$78.778	$78.78	$78.80	$78.80
Purchase #6	$51.35	12.353%	$57.6933	$57.69	$57.70	$57.70
Purchase #7	$37.71	13.694%	$42.874	$42.87	$42.85	$42.90
7 purchase totals =	$643.78		$708.3672	$708.36	$708.40	$708.40