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	$8.27	6.573%	$8.8136	$8.81	$8.80	$8.80
Purchase #2	$41.73	12.474%	$46.9354	$46.94	$46.95	$46.90
Purchase #3	$29.95	5.218%	$31.5128	$31.51	$31.50	$31.50
Purchase #4	$50.38	9.360%	$55.0956	$55.10	$55.10	$55.10
Purchase #5	$87.74	3.155%	$90.5082	$90.51	$90.50	$90.50
Purchase #6	$173.65	4.172%	$180.8947	$180.89	$180.90	$180.90
Purchase #7	$103.50	11.728%	$115.6385	$115.64	$115.65	$115.60
7 purchase totals =	$495.22		$529.3988	$529.40	$529.40	$529.30