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	$6.64	7.548%	$7.1412	$7.14	$7.15	$7.10
Purchase #2	$145.49	13.542%	$165.1923	$165.19	$165.20	$165.20
Purchase #3	$144.65	12.229%	$162.3392	$162.34	$162.35	$162.30
Purchase #4	$174.83	13.446%	$198.3376	$198.34	$198.35	$198.30
Purchase #5	$60.33	12.499%	$67.8706	$67.87	$67.85	$67.90
Purchase #6	$108.48	3.509%	$112.2866	$112.29	$112.30	$112.30
Purchase #7	$219.45	4.309%	$228.9061	$228.91	$228.90	$228.90
7 purchase totals =	$859.87		$942.0736	$942.08	$942.10	$942.00