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	$146.70	8.581%	$159.2883	$159.29	$159.30	$159.30
Purchase #2	$93.70	12.629%	$105.5334	$105.53	$105.55	$105.50
Purchase #3	$40.86	13.556%	$46.399	$46.40	$46.40	$46.40
Purchase #4	$120.54	6.450%	$128.3148	$128.31	$128.30	$128.30
Purchase #5	$227.36	13.167%	$257.2965	$257.30	$257.30	$257.30
Purchase #6	$41.98	3.411%	$43.4119	$43.41	$43.40	$43.40
Purchase #7	$92.50	8.623%	$100.4763	$100.48	$100.50	$100.50
7 purchase totals =	$763.64		$840.7202	$840.72	$840.75	$840.70