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	$124.97	12.404%	$140.4713	$140.47	$140.45	$140.50
Purchase #2	$89.79	5.679%	$94.8892	$94.89	$94.90	$94.90
Purchase #3	$84.62	7.194%	$90.7076	$90.71	$90.70	$90.70
Purchase #4	$50.80	12.614%	$57.2079	$57.21	$57.20	$57.20
Purchase #5	$68.55	6.404%	$72.9399	$72.94	$72.95	$72.90
Purchase #6	$110.38	7.756%	$118.9411	$118.94	$118.95	$118.90
Purchase #7	$91.34	13.401%	$103.5805	$103.58	$103.60	$103.60
7 purchase totals =	$620.45		$678.7375	$678.74	$678.75	$678.70