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	$79.48	12.570%	$89.4706	$89.47	$89.45	$89.50
Purchase #2	$146.25	11.388%	$162.905	$162.91	$162.90	$162.90
Purchase #3	$85.75	13.723%	$97.5175	$97.52	$97.50	$97.50
Purchase #4	$81.33	11.392%	$90.5951	$90.60	$90.60	$90.60
Purchase #5	$77.93	4.367%	$81.3332	$81.33	$81.35	$81.30
Purchase #6	$217.66	11.771%	$243.2808	$243.28	$243.30	$243.30
Purchase #7	$170.25	5.804%	$180.1313	$180.13	$180.15	$180.10
7 purchase totals =	$858.65		$945.2335	$945.24	$945.25	$945.20