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	$136.55	11.632%	$152.4335	$152.43	$152.45	$152.40
Purchase #2	$246.95	5.504%	$260.5421	$260.54	$260.55	$260.50
Purchase #3	$136.48	6.860%	$145.8425	$145.84	$145.85	$145.80
Purchase #4	$159.66	12.510%	$179.6335	$179.63	$179.65	$179.60
Purchase #5	$143.50	8.609%	$155.8539	$155.85	$155.85	$155.90
Purchase #6	$195.46	11.555%	$218.0454	$218.05	$218.05	$218.00
Purchase #7	$97.74	12.137%	$109.6027	$109.60	$109.60	$109.60
7 purchase totals =	$1,116.34		$1,221.9536	$1,221.94	$1,222.00	$1,221.80