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	$10.70	12.467%	$12.034	$12.03	$12.05	$12.00
Purchase #2	$247.43	6.127%	$262.59	$262.59	$262.60	$262.60
Purchase #3	$64.25	4.639%	$67.2306	$67.23	$67.25	$67.20
Purchase #4	$123.38	10.316%	$136.1079	$136.11	$136.10	$136.10
Purchase #5	$240.37	9.868%	$264.0897	$264.09	$264.10	$264.10
Purchase #6	$218.46	3.616%	$226.3595	$226.36	$226.35	$226.40
Purchase #7	$90.59	4.732%	$94.8767	$94.88	$94.90	$94.90
7 purchase totals =	$995.18		$1,063.2884	$1,063.29	$1,063.35	$1,063.30