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	$166.61	13.392%	$188.9224	$188.92	$188.90	$188.90
Purchase #2	$83.33	7.772%	$89.8064	$89.81	$89.80	$89.80
Purchase #3	$225.45	7.146%	$241.5607	$241.56	$241.55	$241.60
Purchase #4	$238.96	10.507%	$264.0675	$264.07	$264.05	$264.10
Purchase #5	$79.68	3.791%	$82.7007	$82.70	$82.70	$82.70
Purchase #6	$108.27	7.614%	$116.5137	$116.51	$116.50	$116.50
Purchase #7	$235.47	5.846%	$249.2356	$249.24	$249.25	$249.20
7 purchase totals =	$1,137.77		$1,232.8070	$1,232.81	$1,232.75	$1,232.80