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	$250.59	12.132%	$280.9916	$280.99	$281.00	$281.00
Purchase #2	$155.86	4.127%	$162.2923	$162.29	$162.30	$162.30
Purchase #3	$19.91	5.661%	$21.0371	$21.04	$21.05	$21.00
Purchase #4	$89.79	4.707%	$94.0164	$94.02	$94.00	$94.00
Purchase #5	$184.51	12.765%	$208.0627	$208.06	$208.05	$208.10
Purchase #6	$82.38	9.870%	$90.5109	$90.51	$90.50	$90.50
Purchase #7	$236.55	11.204%	$263.0531	$263.05	$263.05	$263.10
7 purchase totals =	$1,019.59		$1,119.9641	$1,119.96	$1,119.95	$1,120.00