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	$126.89	3.488%	$131.3159	$131.32	$131.30	$131.30
Purchase #2	$28.63	11.639%	$31.9622	$31.96	$31.95	$32.00
Purchase #3	$188.30	13.103%	$212.9729	$212.97	$212.95	$213.00
Purchase #4	$153.58	7.578%	$165.2183	$165.22	$165.20	$165.20
Purchase #5	$92.43	9.168%	$100.904	$100.90	$100.90	$100.90
Purchase #6	$134.51	6.186%	$142.8308	$142.83	$142.85	$142.80
Purchase #7	$221.81	6.424%	$236.0591	$236.06	$236.05	$236.10
7 purchase totals =	$946.15		$1,021.2632	$1,021.26	$1,021.20	$1,021.30