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	$243.47	13.295%	$275.8393	$275.84	$275.85	$275.80
Purchase #2	$117.66	5.273%	$123.8642	$123.86	$123.85	$123.90
Purchase #3	$83.50	7.352%	$89.6389	$89.64	$89.65	$89.60
Purchase #4	$69.99	3.324%	$72.3165	$72.32	$72.30	$72.30
Purchase #5	$22.63	5.696%	$23.919	$23.92	$23.90	$23.90
Purchase #6	$57.25	9.355%	$62.6057	$62.61	$62.60	$62.60
Purchase #7	$169.79	7.396%	$182.3477	$182.35	$182.35	$182.30
7 purchase totals =	$764.29		$830.5313	$830.54	$830.50	$830.40