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	$96.51	3.447%	$99.8367	$99.84	$99.85	$99.80
Purchase #2	$87.85	13.192%	$99.4392	$99.44	$99.45	$99.40
Purchase #3	$169.31	4.288%	$176.57	$176.57	$176.55	$176.60
Purchase #4	$188.80	3.222%	$194.8831	$194.88	$194.90	$194.90
Purchase #5	$181.79	10.218%	$200.3653	$200.37	$200.35	$200.40
Purchase #6	$159.72	9.179%	$174.3807	$174.38	$174.40	$174.40
Purchase #7	$48.91	10.263%	$53.9296	$53.93	$53.95	$53.90
7 purchase totals =	$932.89		$999.4046	$999.41	$999.45	$999.40