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	$176.75	6.851%	$188.8591	$188.86	$188.85	$188.90
Purchase #2	$147.52	6.352%	$156.8905	$156.89	$156.90	$156.90
Purchase #3	$60.41	10.625%	$66.8286	$66.83	$66.85	$66.80
Purchase #4	$119.40	9.815%	$131.1191	$131.12	$131.10	$131.10
Purchase #5	$144.49	7.538%	$155.3817	$155.38	$155.40	$155.40
Purchase #6	$140.87	3.623%	$145.9737	$145.97	$145.95	$146.00
Purchase #7	$146.92	9.402%	$160.7334	$160.73	$160.75	$160.70
7 purchase totals =	$936.36		$1,005.7861	$1,005.78	$1,005.80	$1,005.80