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	$26.47	7.644%	$28.4934	$28.49	$28.50	$28.50
Purchase #2	$168.97	3.205%	$174.3855	$174.39	$174.40	$174.40
Purchase #3	$248.89	12.333%	$279.5856	$279.59	$279.60	$279.60
Purchase #4	$53.73	9.773%	$58.981	$58.98	$59.00	$59.00
Purchase #5	$83.96	12.153%	$94.1637	$94.16	$94.15	$94.20
Purchase #6	$63.84	12.661%	$71.9228	$71.92	$71.90	$71.90
Purchase #7	$41.49	13.308%	$47.0115	$47.01	$47.00	$47.00
7 purchase totals =	$687.35		$754.5435	$754.54	$754.55	$754.60