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	$37.62	13.265%	$42.6103	$42.61	$42.60	$42.60
Purchase #2	$115.74	8.245%	$125.2828	$125.28	$125.30	$125.30
Purchase #3	$144.71	9.544%	$158.5211	$158.52	$158.50	$158.50
Purchase #4	$81.81	9.144%	$89.2907	$89.29	$89.30	$89.30
Purchase #5	$114.33	8.747%	$124.3304	$124.33	$124.35	$124.30
Purchase #6	$201.74	6.622%	$215.0992	$215.10	$215.10	$215.10
Purchase #7	$194.59	8.220%	$210.5853	$210.59	$210.60	$210.60
7 purchase totals =	$890.54		$965.7198	$965.72	$965.75	$965.70