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	$49.80	7.857%	$53.7128	$53.71	$53.70	$53.70
Purchase #2	$101.29	12.714%	$114.168	$114.17	$114.15	$114.20
Purchase #3	$187.45	10.138%	$206.4537	$206.45	$206.45	$206.50
Purchase #4	$81.78	10.540%	$90.3996	$90.40	$90.40	$90.40
Purchase #5	$242.56	12.690%	$273.3409	$273.34	$273.35	$273.30
Purchase #6	$93.46	12.809%	$105.4313	$105.43	$105.45	$105.40
Purchase #7	$238.98	3.293%	$246.8496	$246.85	$246.85	$246.80
7 purchase totals =	$995.32		$1,090.3559	$1,090.35	$1,090.35	$1,090.30