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	$61.85	12.730%	$69.7235	$69.72	$69.70	$69.70
Purchase #2	$154.84	12.508%	$174.2074	$174.21	$174.20	$174.20
Purchase #3	$201.51	11.466%	$224.6151	$224.62	$224.60	$224.60
Purchase #4	$210.94	4.710%	$220.8753	$220.88	$220.90	$220.90
Purchase #5	$249.89	11.800%	$279.377	$279.38	$279.40	$279.40
Purchase #6	$109.32	6.372%	$116.2859	$116.29	$116.30	$116.30
Purchase #7	$14.98	5.217%	$15.7615	$15.76	$15.75	$15.80
7 purchase totals =	$1,003.33		$1,100.8457	$1,100.86	$1,100.85	$1,100.90