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	$70.35	12.122%	$78.8778	$78.88	$78.90	$78.90
Purchase #2	$113.39	6.176%	$120.393	$120.39	$120.40	$120.40
Purchase #3	$234.37	4.453%	$244.8065	$244.81	$244.80	$244.80
Purchase #4	$231.27	6.117%	$245.4168	$245.42	$245.40	$245.40
Purchase #5	$67.68	7.432%	$72.71	$72.71	$72.70	$72.70
Purchase #6	$105.27	3.351%	$108.7976	$108.80	$108.80	$108.80
Purchase #7	$93.34	6.561%	$99.464	$99.46	$99.45	$99.50
7 purchase totals =	$915.67		$970.4657	$970.47	$970.45	$970.50