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	$47.25	8.822%	$51.4184	$51.42	$51.40	$51.40
Purchase #2	$115.57	7.200%	$123.891	$123.89	$123.90	$123.90
Purchase #3	$138.78	4.315%	$144.7684	$144.77	$144.75	$144.80
Purchase #4	$20.74	10.607%	$22.9399	$22.94	$22.95	$22.90
Purchase #5	$189.88	7.118%	$203.3957	$203.40	$203.40	$203.40
Purchase #6	$73.55	10.671%	$81.3985	$81.40	$81.40	$81.40
Purchase #7	$190.41	3.202%	$196.5069	$196.51	$196.50	$196.50
7 purchase totals =	$776.18		$824.3188	$824.33	$824.30	$824.30