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	$171.60	8.474%	$186.1414	$186.14	$186.15	$186.10
Purchase #2	$25.76	9.563%	$28.2234	$28.22	$28.20	$28.20
Purchase #3	$239.68	10.811%	$265.5918	$265.59	$265.60	$265.60
Purchase #4	$215.66	12.832%	$243.3335	$243.33	$243.35	$243.30
Purchase #5	$18.38	11.123%	$20.4244	$20.42	$20.40	$20.40
Purchase #6	$152.84	9.293%	$167.0434	$167.04	$167.05	$167.00
Purchase #7	$57.28	3.821%	$59.4687	$59.47	$59.45	$59.50
7 purchase totals =	$881.20		$970.2266	$970.21	$970.20	$970.10