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	$52.33	3.828%	$54.3332	$54.33	$54.35	$54.30
Purchase #2	$136.67	10.646%	$151.2199	$151.22	$151.20	$151.20
Purchase #3	$137.61	10.296%	$151.7783	$151.78	$151.80	$151.80
Purchase #4	$36.30	3.488%	$37.5661	$37.57	$37.55	$37.60
Purchase #5	$88.26	3.420%	$91.2785	$91.28	$91.30	$91.30
Purchase #6	$120.51	8.368%	$130.5943	$130.59	$130.60	$130.60
Purchase #7	$89.30	5.245%	$93.9838	$93.98	$94.00	$94.00
7 purchase totals =	$660.98		$710.7541	$710.75	$710.80	$710.80