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	$92.86	6.144%	$98.5653	$98.57	$98.55	$98.60
Purchase #2	$144.76	8.304%	$156.7809	$156.78	$156.80	$156.80
Purchase #3	$238.91	6.824%	$255.2132	$255.21	$255.20	$255.20
Purchase #4	$136.46	10.194%	$150.3707	$150.37	$150.35	$150.40
Purchase #5	$237.75	3.245%	$245.465	$245.47	$245.45	$245.50
Purchase #6	$72.25	3.514%	$74.7889	$74.79	$74.80	$74.80
Purchase #7	$55.41	12.410%	$62.2864	$62.29	$62.30	$62.30
7 purchase totals =	$978.40		$1,043.4704	$1,043.48	$1,043.45	$1,043.60