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	$228.78	4.215%	$238.4231	$238.42	$238.40	$238.40
Purchase #2	$81.67	9.526%	$89.4499	$89.45	$89.45	$89.40
Purchase #3	$233.43	9.444%	$255.4751	$255.48	$255.50	$255.50
Purchase #4	$240.51	6.359%	$255.804	$255.80	$255.80	$255.80
Purchase #5	$62.94	7.736%	$67.809	$67.81	$67.80	$67.80
Purchase #6	$54.50	12.824%	$61.4891	$61.49	$61.50	$61.50
Purchase #7	$224.59	8.556%	$243.8059	$243.81	$243.80	$243.80
7 purchase totals =	$1,126.42		$1,212.2561	$1,212.26	$1,212.25	$1,212.20