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	$72.86	7.383%	$78.2393	$78.24	$78.25	$78.20
Purchase #2	$221.45	3.679%	$229.5971	$229.60	$229.60	$229.60
Purchase #3	$222.26	11.328%	$247.4376	$247.44	$247.45	$247.40
Purchase #4	$202.66	3.433%	$209.6173	$209.62	$209.60	$209.60
Purchase #5	$113.34	5.400%	$119.4604	$119.46	$119.45	$119.50
Purchase #6	$50.82	6.162%	$53.9515	$53.95	$53.95	$54.00
Purchase #7	$38.47	5.433%	$40.5601	$40.56	$40.55	$40.60
7 purchase totals =	$921.86		$978.8633	$978.87	$978.85	$978.90