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	$55.85	6.788%	$59.6411	$59.64	$59.65	$59.60
Purchase #2	$166.87	12.803%	$188.2344	$188.23	$188.25	$188.20
Purchase #3	$152.30	5.447%	$160.5958	$160.60	$160.60	$160.60
Purchase #4	$67.83	8.414%	$73.5372	$73.54	$73.55	$73.50
Purchase #5	$59.25	12.680%	$66.7629	$66.76	$66.75	$66.80
Purchase #6	$193.73	10.354%	$213.7888	$213.79	$213.80	$213.80
Purchase #7	$238.70	10.790%	$264.4557	$264.46	$264.45	$264.50
7 purchase totals =	$934.53		$1,027.0159	$1,027.02	$1,027.05	$1,027.00