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	$249.91	5.551%	$263.7825	$263.78	$263.80	$263.80
Purchase #2	$59.47	5.743%	$62.8854	$62.89	$62.90	$62.90
Purchase #3	$86.58	11.524%	$96.5575	$96.56	$96.55	$96.60
Purchase #4	$65.42	3.842%	$67.9334	$67.93	$67.95	$67.90
Purchase #5	$79.74	7.218%	$85.4956	$85.50	$85.50	$85.50
Purchase #6	$219.94	8.602%	$238.8592	$238.86	$238.85	$238.90
Purchase #7	$248.42	9.780%	$272.7155	$272.72	$272.70	$272.70
7 purchase totals =	$1,009.48		$1,088.2291	$1,088.24	$1,088.25	$1,088.30