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	$40.31	5.544%	$42.5448	$42.54	$42.55	$42.50
Purchase #2	$36.64	3.855%	$38.0525	$38.05	$38.05	$38.10
Purchase #3	$196.68	10.266%	$216.8712	$216.87	$216.85	$216.90
Purchase #4	$143.46	10.144%	$158.0126	$158.01	$158.00	$158.00
Purchase #5	$130.65	3.655%	$135.4253	$135.43	$135.45	$135.40
Purchase #6	$123.55	6.250%	$131.2719	$131.27	$131.25	$131.30
Purchase #7	$115.89	13.365%	$131.3787	$131.38	$131.40	$131.40
7 purchase totals =	$787.18		$853.5570	$853.55	$853.55	$853.60