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	$81.72	9.451%	$89.4434	$89.44	$89.45	$89.40
Purchase #2	$210.52	12.732%	$237.3234	$237.32	$237.30	$237.30
Purchase #3	$209.35	12.227%	$234.9472	$234.95	$234.95	$234.90
Purchase #4	$228.34	5.688%	$241.328	$241.33	$241.35	$241.30
Purchase #5	$141.75	7.629%	$152.5641	$152.56	$152.55	$152.60
Purchase #6	$213.81	12.679%	$240.919	$240.92	$240.90	$240.90
Purchase #7	$179.35	6.102%	$190.2939	$190.29	$190.30	$190.30
7 purchase totals =	$1,264.84		$1,386.8190	$1,386.81	$1,386.80	$1,386.70