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	$74.90	11.453%	$83.4783	$83.48	$83.50	$83.50
Purchase #2	$10.90	9.413%	$11.926	$11.93	$11.95	$11.90
Purchase #3	$71.67	12.382%	$80.5442	$80.54	$80.55	$80.50
Purchase #4	$48.80	13.338%	$55.3089	$55.31	$55.30	$55.30
Purchase #5	$247.89	11.399%	$276.147	$276.15	$276.15	$276.10
Purchase #6	$186.98	12.149%	$209.6962	$209.70	$209.70	$209.70
Purchase #7	$37.78	10.604%	$41.7862	$41.79	$41.80	$41.80
7 purchase totals =	$678.92		$758.8868	$758.90	$758.95	$758.80