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	$96.64	3.496%	$100.0185	$100.02	$100.00	$100.00
Purchase #2	$49.48	3.655%	$51.2885	$51.29	$51.30	$51.30
Purchase #3	$128.83	6.202%	$136.82	$136.82	$136.80	$136.80
Purchase #4	$165.69	10.179%	$182.5556	$182.56	$182.55	$182.60
Purchase #5	$132.32	7.520%	$142.2705	$142.27	$142.25	$142.30
Purchase #6	$119.43	5.187%	$125.6248	$125.62	$125.60	$125.60
Purchase #7	$142.70	5.212%	$150.1375	$150.14	$150.15	$150.10
7 purchase totals =	$835.09		$888.7154	$888.72	$888.65	$888.70