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	$39.46	4.368%	$41.1836	$41.18	$41.20	$41.20
Purchase #2	$58.38	7.204%	$62.5857	$62.59	$62.60	$62.60
Purchase #3	$55.54	5.408%	$58.5436	$58.54	$58.55	$58.50
Purchase #4	$67.91	4.278%	$70.8152	$70.82	$70.80	$70.80
Purchase #5	$236.61	8.570%	$256.8875	$256.89	$256.90	$256.90
Purchase #6	$151.29	10.789%	$167.6127	$167.61	$167.60	$167.60
Purchase #7	$191.56	5.698%	$202.4751	$202.48	$202.50	$202.50
7 purchase totals =	$800.75		$860.1034	$860.11	$860.15	$860.10