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	$52.40	7.140%	$56.1414	$56.14	$56.15	$56.10
Purchase #2	$244.48	5.726%	$258.4789	$258.48	$258.50	$258.50
Purchase #3	$203.83	12.604%	$229.5207	$229.52	$229.50	$229.50
Purchase #4	$67.89	13.642%	$77.1516	$77.15	$77.15	$77.20
Purchase #5	$51.50	3.781%	$53.4472	$53.45	$53.45	$53.40
Purchase #6	$162.45	12.362%	$182.5321	$182.53	$182.55	$182.50
Purchase #7	$71.83	10.822%	$79.6034	$79.60	$79.60	$79.60
7 purchase totals =	$854.38		$936.8753	$936.87	$936.90	$936.80