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	$114.86	12.846%	$129.6149	$129.61	$129.60	$129.60
Purchase #2	$131.49	4.102%	$136.8837	$136.88	$136.90	$136.90
Purchase #3	$57.55	3.526%	$59.5792	$59.58	$59.60	$59.60
Purchase #4	$70.73	9.668%	$77.5682	$77.57	$77.55	$77.60
Purchase #5	$161.30	6.647%	$172.0216	$172.02	$172.00	$172.00
Purchase #6	$136.60	3.200%	$140.9712	$140.97	$140.95	$141.00
Purchase #7	$136.71	11.435%	$152.3428	$152.34	$152.35	$152.30
7 purchase totals =	$809.24		$868.9816	$868.97	$868.95	$869.00