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	$193.58	9.683%	$212.3244	$212.32	$212.30	$212.30
Purchase #2	$97.69	10.789%	$108.2298	$108.23	$108.25	$108.20
Purchase #3	$78.96	8.116%	$85.3684	$85.37	$85.35	$85.40
Purchase #4	$131.55	3.722%	$136.4463	$136.45	$136.45	$136.40
Purchase #5	$30.45	10.794%	$33.7368	$33.74	$33.75	$33.70
Purchase #6	$194.66	3.242%	$200.9709	$200.97	$200.95	$201.00
Purchase #7	$248.32	10.144%	$273.5096	$273.51	$273.50	$273.50
7 purchase totals =	$975.21		$1,050.5862	$1,050.59	$1,050.55	$1,050.50