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	$48.25	10.325%	$53.2318	$53.23	$53.25	$53.20
Purchase #2	$91.62	5.797%	$96.9312	$96.93	$96.95	$96.90
Purchase #3	$85.48	13.393%	$96.9283	$96.93	$96.95	$96.90
Purchase #4	$39.87	7.744%	$42.9575	$42.96	$42.95	$43.00
Purchase #5	$78.53	9.486%	$85.9794	$85.98	$86.00	$86.00
Purchase #6	$38.30	9.448%	$41.9186	$41.92	$41.90	$41.90
Purchase #7	$74.57	11.704%	$83.2977	$83.30	$83.30	$83.30
7 purchase totals =	$456.62		$501.2445	$501.25	$501.30	$501.20