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	$98.97	12.444%	$111.2858	$111.29	$111.30	$111.30
Purchase #2	$64.27	9.341%	$70.2735	$70.27	$70.25	$70.30
Purchase #3	$99.90	4.533%	$104.4285	$104.43	$104.45	$104.40
Purchase #4	$149.90	13.432%	$170.0346	$170.03	$170.05	$170.00
Purchase #5	$80.27	9.438%	$87.8459	$87.85	$87.85	$87.80
Purchase #6	$145.39	9.490%	$159.1875	$159.19	$159.20	$159.20
Purchase #7	$73.30	12.296%	$82.313	$82.31	$82.30	$82.30
7 purchase totals =	$712.00		$785.3688	$785.37	$785.40	$785.30