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	$75.44	3.848%	$78.3429	$78.34	$78.35	$78.30
Purchase #2	$88.54	4.366%	$92.4057	$92.41	$92.40	$92.40
Purchase #3	$178.49	12.575%	$200.9351	$200.94	$200.95	$200.90
Purchase #4	$144.98	5.180%	$152.49	$152.49	$152.50	$152.50
Purchase #5	$249.74	12.381%	$280.6603	$280.66	$280.65	$280.70
Purchase #6	$146.85	7.760%	$158.2456	$158.25	$158.25	$158.20
Purchase #7	$152.46	10.482%	$168.4409	$168.44	$168.45	$168.40
7 purchase totals =	$1,036.50		$1,131.5205	$1,131.53	$1,131.55	$1,131.40