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	$16.98	8.656%	$18.4498	$18.45	$18.45	$18.40
Purchase #2	$70.65	11.817%	$78.9987	$79.00	$79.00	$79.00
Purchase #3	$168.58	12.656%	$189.9155	$189.92	$189.90	$189.90
Purchase #4	$40.59	13.123%	$45.9166	$45.92	$45.90	$45.90
Purchase #5	$68.84	5.799%	$72.832	$72.83	$72.85	$72.80
Purchase #6	$26.31	9.405%	$28.7845	$28.78	$28.80	$28.80
Purchase #7	$249.92	6.370%	$265.8399	$265.84	$265.85	$265.80
7 purchase totals =	$641.87		$700.7370	$700.74	$700.75	$700.60