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	$125.46	12.263%	$140.8452	$140.85	$140.85	$140.80
Purchase #2	$56.27	10.637%	$62.2554	$62.26	$62.25	$62.30
Purchase #3	$207.67	13.441%	$235.5829	$235.58	$235.60	$235.60
Purchase #4	$94.81	4.741%	$99.3049	$99.30	$99.30	$99.30
Purchase #5	$142.89	4.224%	$148.9257	$148.93	$148.95	$148.90
Purchase #6	$102.70	9.630%	$112.59	$112.59	$112.60	$112.60
Purchase #7	$47.76	8.151%	$51.6529	$51.65	$51.65	$51.70
7 purchase totals =	$777.56		$851.1570	$851.16	$851.20	$851.20