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	$21.87	13.323%	$24.7837	$24.78	$24.80	$24.80
Purchase #2	$71.64	4.281%	$74.7069	$74.71	$74.70	$74.70
Purchase #3	$25.33	10.389%	$27.9615	$27.96	$27.95	$28.00
Purchase #4	$69.48	4.507%	$72.6115	$72.61	$72.60	$72.60
Purchase #5	$212.68	9.383%	$232.6358	$232.64	$232.65	$232.60
Purchase #6	$77.28	6.498%	$82.3017	$82.30	$82.30	$82.30
Purchase #7	$80.27	12.718%	$90.4787	$90.48	$90.50	$90.50
7 purchase totals =	$558.55		$605.4798	$605.48	$605.50	$605.50