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	$93.81	5.832%	$99.281	$99.28	$99.30	$99.30
Purchase #2	$100.72	4.825%	$105.5797	$105.58	$105.60	$105.60
Purchase #3	$159.85	3.245%	$165.0371	$165.04	$165.05	$165.00
Purchase #4	$125.56	12.545%	$141.3115	$141.31	$141.30	$141.30
Purchase #5	$89.61	12.648%	$100.9439	$100.94	$100.95	$100.90
Purchase #6	$177.72	9.214%	$194.0951	$194.10	$194.10	$194.10
Purchase #7	$121.34	3.262%	$125.2981	$125.30	$125.30	$125.30
7 purchase totals =	$868.61		$931.5464	$931.55	$931.60	$931.50