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	$72.77	7.572%	$78.2801	$78.28	$78.30	$78.30
Purchase #2	$41.30	3.668%	$42.8149	$42.81	$42.80	$42.80
Purchase #3	$151.96	7.627%	$163.55	$163.55	$163.55	$163.60
Purchase #4	$97.89	3.378%	$101.1967	$101.20	$101.20	$101.20
Purchase #5	$6.81	6.823%	$7.2746	$7.27	$7.25	$7.30
Purchase #6	$97.38	3.600%	$100.8857	$100.89	$100.90	$100.90
Purchase #7	$25.52	3.851%	$26.5028	$26.50	$26.50	$26.50
7 purchase totals =	$493.63		$520.5048	$520.50	$520.50	$520.60