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	$31.46	7.802%	$33.9145	$33.91	$33.90	$33.90
Purchase #2	$151.57	4.655%	$158.6256	$158.63	$158.65	$158.60
Purchase #3	$206.61	4.123%	$215.1285	$215.13	$215.15	$215.10
Purchase #4	$132.90	5.828%	$140.6454	$140.65	$140.65	$140.60
Purchase #5	$59.34	5.873%	$62.825	$62.83	$62.85	$62.80
Purchase #6	$96.65	9.488%	$105.8202	$105.82	$105.80	$105.80
Purchase #7	$190.89	6.745%	$203.7655	$203.77	$203.75	$203.80
7 purchase totals =	$869.42		$920.7247	$920.74	$920.75	$920.60