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	$81.52	9.734%	$89.4552	$89.46	$89.45	$89.50
Purchase #2	$201.47	11.460%	$224.5585	$224.56	$224.55	$224.60
Purchase #3	$162.75	12.349%	$182.848	$182.85	$182.85	$182.80
Purchase #4	$247.87	10.335%	$273.4874	$273.49	$273.50	$273.50
Purchase #5	$55.41	10.273%	$61.1023	$61.10	$61.10	$61.10
Purchase #6	$115.86	10.546%	$128.0786	$128.08	$128.10	$128.10
Purchase #7	$165.97	12.111%	$186.0706	$186.07	$186.05	$186.10
7 purchase totals =	$1,030.85		$1,145.6006	$1,145.61	$1,145.60	$1,145.70