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	$29.29	8.449%	$31.7647	$31.76	$31.75	$31.80
Purchase #2	$186.94	4.218%	$194.8251	$194.83	$194.85	$194.80
Purchase #3	$13.64	13.261%	$15.4488	$15.45	$15.45	$15.40
Purchase #4	$57.83	10.342%	$63.8108	$63.81	$63.80	$63.80
Purchase #5	$90.93	5.121%	$95.5865	$95.59	$95.60	$95.60
Purchase #6	$168.41	13.867%	$191.7634	$191.76	$191.75	$191.80
Purchase #7	$153.38	11.705%	$171.3331	$171.33	$171.35	$171.30
7 purchase totals =	$700.42		$764.5324	$764.53	$764.55	$764.50