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	$68.72	6.280%	$73.0356	$73.04	$73.05	$73.00
Purchase #2	$61.71	10.827%	$68.3913	$68.39	$68.40	$68.40
Purchase #3	$235.32	8.616%	$255.5952	$255.60	$255.60	$255.60
Purchase #4	$184.70	6.627%	$196.9401	$196.94	$196.95	$196.90
Purchase #5	$68.60	4.107%	$71.4174	$71.42	$71.40	$71.40
Purchase #6	$188.59	8.115%	$203.8941	$203.89	$203.90	$203.90
Purchase #7	$78.64	4.458%	$82.1458	$82.15	$82.15	$82.10
7 purchase totals =	$886.28		$951.4195	$951.43	$951.45	$951.30