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	$48.91	9.118%	$53.3696	$53.37	$53.35	$53.40
Purchase #2	$101.76	10.157%	$112.0958	$112.10	$112.10	$112.10
Purchase #3	$84.88	12.129%	$95.1751	$95.18	$95.20	$95.20
Purchase #4	$16.65	8.761%	$18.1087	$18.11	$18.10	$18.10
Purchase #5	$118.83	7.131%	$127.3038	$127.30	$127.30	$127.30
Purchase #6	$209.40	9.111%	$228.4784	$228.48	$228.50	$228.50
Purchase #7	$24.73	12.857%	$27.9095	$27.91	$27.90	$27.90
7 purchase totals =	$605.16		$662.4409	$662.45	$662.45	$662.50