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	$64.70	12.387%	$72.7144	$72.71	$72.70	$72.70
Purchase #2	$104.78	3.432%	$108.376	$108.38	$108.40	$108.40
Purchase #3	$124.76	10.825%	$138.2653	$138.27	$138.25	$138.30
Purchase #4	$18.96	11.524%	$21.145	$21.15	$21.15	$21.10
Purchase #5	$155.28	7.485%	$166.9027	$166.90	$166.90	$166.90
Purchase #6	$160.55	4.464%	$167.717	$167.72	$167.70	$167.70
Purchase #7	$195.54	10.156%	$215.399	$215.40	$215.40	$215.40
7 purchase totals =	$824.57		$890.5194	$890.53	$890.50	$890.50