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	$137.91	9.419%	$150.8997	$150.90	$150.90	$150.90
Purchase #2	$249.96	6.219%	$265.505	$265.51	$265.50	$265.50
Purchase #3	$53.81	6.811%	$57.475	$57.48	$57.50	$57.50
Purchase #4	$111.71	11.688%	$124.7667	$124.77	$124.75	$124.80
Purchase #5	$44.87	8.142%	$48.5233	$48.52	$48.50	$48.50
Purchase #6	$104.59	11.708%	$116.8354	$116.84	$116.85	$116.80
Purchase #7	$171.35	10.501%	$189.3435	$189.34	$189.35	$189.30
7 purchase totals =	$874.20		$953.3486	$953.36	$953.35	$953.30