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	$37.77	3.459%	$39.0765	$39.08	$39.10	$39.10
Purchase #2	$85.85	6.121%	$91.1049	$91.10	$91.10	$91.10
Purchase #3	$93.84	6.146%	$99.6074	$99.61	$99.60	$99.60
Purchase #4	$114.77	6.833%	$122.6122	$122.61	$122.60	$122.60
Purchase #5	$218.58	9.466%	$239.2708	$239.27	$239.25	$239.30
Purchase #6	$65.76	10.263%	$72.5089	$72.51	$72.50	$72.50
Purchase #7	$128.94	9.765%	$141.531	$141.53	$141.55	$141.50
7 purchase totals =	$745.51		$805.7117	$805.71	$805.70	$805.70