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	$108.45	9.229%	$118.4589	$118.46	$118.45	$118.50
Purchase #2	$178.45	10.287%	$196.8072	$196.81	$196.80	$196.80
Purchase #3	$155.40	13.147%	$175.8304	$175.83	$175.85	$175.80
Purchase #4	$55.50	7.230%	$59.5127	$59.51	$59.50	$59.50
Purchase #5	$199.35	5.224%	$209.764	$209.76	$209.75	$209.80
Purchase #6	$189.38	9.350%	$207.087	$207.09	$207.10	$207.10
Purchase #7	$57.62	4.264%	$60.0769	$60.08	$60.10	$60.10
7 purchase totals =	$944.15		$1,027.5371	$1,027.54	$1,027.55	$1,027.60