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	$38.51	11.306%	$42.8639	$42.86	$42.85	$42.90
Purchase #2	$220.74	8.676%	$239.8914	$239.89	$239.90	$239.90
Purchase #3	$212.47	13.156%	$240.4226	$240.42	$240.40	$240.40
Purchase #4	$203.59	4.740%	$213.2402	$213.24	$213.25	$213.20
Purchase #5	$196.82	6.787%	$210.1782	$210.18	$210.20	$210.20
Purchase #6	$65.57	11.242%	$72.9414	$72.94	$72.95	$72.90
Purchase #7	$19.29	9.635%	$21.1486	$21.15	$21.15	$21.10
7 purchase totals =	$956.99		$1,040.6863	$1,040.68	$1,040.70	$1,040.60