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	$118.44	8.564%	$128.5832	$128.58	$128.60	$128.60
Purchase #2	$58.74	4.304%	$61.2682	$61.27	$61.25	$61.30
Purchase #3	$154.55	13.181%	$174.9212	$174.92	$174.90	$174.90
Purchase #4	$42.78	13.475%	$48.5446	$48.54	$48.55	$48.50
Purchase #5	$191.76	3.428%	$198.3335	$198.33	$198.35	$198.30
Purchase #6	$79.32	12.380%	$89.1398	$89.14	$89.15	$89.10
Purchase #7	$125.71	8.193%	$136.0094	$136.01	$136.00	$136.00
7 purchase totals =	$771.30		$836.7999	$836.79	$836.80	$836.70