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	$75.41	3.437%	$78.0018	$78.00	$78.00	$78.00
Purchase #2	$71.96	3.336%	$74.3606	$74.36	$74.35	$74.40
Purchase #3	$80.99	11.678%	$90.448	$90.45	$90.45	$90.40
Purchase #4	$112.80	9.496%	$123.5115	$123.51	$123.50	$123.50
Purchase #5	$110.53	6.806%	$118.0527	$118.05	$118.05	$118.10
Purchase #6	$135.77	10.418%	$149.9145	$149.91	$149.90	$149.90
Purchase #7	$34.88	11.124%	$38.7601	$38.76	$38.75	$38.80
7 purchase totals =	$622.34		$673.0492	$673.04	$673.00	$673.10