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	$18.96	13.767%	$21.5702	$21.57	$21.55	$21.60
Purchase #2	$109.73	4.443%	$114.6053	$114.61	$114.60	$114.60
Purchase #3	$231.78	13.809%	$263.7865	$263.79	$263.80	$263.80
Purchase #4	$148.49	11.171%	$165.0778	$165.08	$165.10	$165.10
Purchase #5	$181.70	4.595%	$190.0491	$190.05	$190.05	$190.00
Purchase #6	$171.77	10.123%	$189.1583	$189.16	$189.15	$189.20
Purchase #7	$172.35	11.139%	$191.5481	$191.55	$191.55	$191.50
7 purchase totals =	$1,034.78		$1,135.7953	$1,135.81	$1,135.80	$1,135.80