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	$102.87	5.789%	$108.8251	$108.83	$108.85	$108.80
Purchase #2	$78.64	13.835%	$89.5198	$89.52	$89.50	$89.50
Purchase #3	$232.48	11.297%	$258.7433	$258.74	$258.75	$258.70
Purchase #4	$133.40	6.220%	$141.6975	$141.70	$141.70	$141.70
Purchase #5	$157.99	4.462%	$165.0395	$165.04	$165.05	$165.00
Purchase #6	$114.96	3.684%	$119.1951	$119.20	$119.20	$119.20
Purchase #7	$79.99	13.597%	$90.8662	$90.87	$90.85	$90.90
7 purchase totals =	$900.33		$973.8865	$973.90	$973.90	$973.80