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	$8.78	12.282%	$9.8584	$9.86	$9.85	$9.90
Purchase #2	$116.56	9.143%	$127.2171	$127.22	$127.20	$127.20
Purchase #3	$86.94	6.841%	$92.8876	$92.89	$92.90	$92.90
Purchase #4	$88.53	11.186%	$98.433	$98.43	$98.45	$98.40
Purchase #5	$135.35	12.470%	$152.2281	$152.23	$152.25	$152.20
Purchase #6	$41.48	10.271%	$45.7404	$45.74	$45.75	$45.70
Purchase #7	$163.86	13.526%	$186.0237	$186.02	$186.00	$186.00
7 purchase totals =	$641.50		$712.3883	$712.39	$712.40	$712.30