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	$231.61	12.139%	$259.7251	$259.73	$259.75	$259.70
Purchase #2	$67.39	5.178%	$70.8795	$70.88	$70.90	$70.90
Purchase #3	$8.48	11.837%	$9.4838	$9.48	$9.50	$9.50
Purchase #4	$187.72	8.217%	$203.145	$203.15	$203.15	$203.10
Purchase #5	$99.84	11.412%	$111.2337	$111.23	$111.25	$111.20
Purchase #6	$170.79	6.506%	$181.9016	$181.90	$181.90	$181.90
Purchase #7	$103.93	5.767%	$109.9236	$109.92	$109.90	$109.90
7 purchase totals =	$869.76		$946.2923	$946.29	$946.35	$946.20