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	$166.59	7.210%	$178.6011	$178.60	$178.60	$178.60
Purchase #2	$53.27	3.830%	$55.3102	$55.31	$55.30	$55.30
Purchase #3	$104.63	10.358%	$115.4676	$115.47	$115.45	$115.50
Purchase #4	$240.58	7.582%	$258.8208	$258.82	$258.80	$258.80
Purchase #5	$54.67	13.198%	$61.8853	$61.89	$61.90	$61.90
Purchase #6	$36.86	12.729%	$41.5519	$41.55	$41.55	$41.60
Purchase #7	$199.81	8.191%	$216.1764	$216.18	$216.20	$216.20
7 purchase totals =	$856.41		$927.8133	$927.82	$927.80	$927.90