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	$81.90	3.842%	$85.0466	$85.05	$85.05	$85.00
Purchase #2	$93.28	10.254%	$102.8449	$102.84	$102.85	$102.80
Purchase #3	$165.57	13.856%	$188.5114	$188.51	$188.50	$188.50
Purchase #4	$235.69	9.765%	$258.7051	$258.71	$258.70	$258.70
Purchase #5	$51.31	13.788%	$58.3846	$58.38	$58.40	$58.40
Purchase #6	$174.77	7.863%	$188.5122	$188.51	$188.50	$188.50
Purchase #7	$160.52	13.717%	$182.5385	$182.54	$182.55	$182.50
7 purchase totals =	$963.04		$1,064.5433	$1,064.54	$1,064.55	$1,064.40