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	$127.27	11.721%	$142.1873	$142.19	$142.20	$142.20
Purchase #2	$46.35	12.188%	$51.9991	$52.00	$52.00	$52.00
Purchase #3	$20.92	3.872%	$21.73	$21.73	$21.75	$21.70
Purchase #4	$141.35	13.416%	$160.3135	$160.31	$160.30	$160.30
Purchase #5	$54.30	10.340%	$59.9146	$59.91	$59.90	$59.90
Purchase #6	$216.88	10.147%	$238.8868	$238.89	$238.90	$238.90
Purchase #7	$103.34	12.329%	$116.0808	$116.08	$116.10	$116.10
7 purchase totals =	$710.41		$791.1121	$791.11	$791.15	$791.10