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	$136.68	11.559%	$152.4788	$152.48	$152.50	$152.50
Purchase #2	$163.79	9.225%	$178.8996	$178.90	$178.90	$178.90
Purchase #3	$51.59	11.430%	$57.4867	$57.49	$57.50	$57.50
Purchase #4	$232.58	5.737%	$245.9231	$245.92	$245.90	$245.90
Purchase #5	$233.44	4.447%	$243.8211	$243.82	$243.80	$243.80
Purchase #6	$50.78	10.115%	$55.9164	$55.92	$55.90	$55.90
Purchase #7	$75.52	9.267%	$82.5184	$82.52	$82.50	$82.50
7 purchase totals =	$944.38		$1,017.0441	$1,017.05	$1,017.00	$1,017.00