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	$35.89	7.474%	$38.5724	$38.57	$38.55	$38.60
Purchase #2	$201.45	11.615%	$224.8484	$224.85	$224.85	$224.80
Purchase #3	$147.76	11.604%	$164.9061	$164.91	$164.90	$164.90
Purchase #4	$137.45	7.575%	$147.8618	$147.86	$147.85	$147.90
Purchase #5	$68.27	5.513%	$72.0337	$72.03	$72.05	$72.00
Purchase #6	$83.45	13.374%	$94.6106	$94.61	$94.60	$94.60
Purchase #7	$145.55	13.565%	$165.2939	$165.29	$165.30	$165.30
7 purchase totals =	$819.82		$908.1269	$908.12	$908.10	$908.10