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	$72.47	8.136%	$78.3662	$78.37	$78.35	$78.40
Purchase #2	$158.56	4.307%	$165.3892	$165.39	$165.40	$165.40
Purchase #3	$13.81	8.678%	$15.0084	$15.01	$15.00	$15.00
Purchase #4	$212.33	3.700%	$220.1862	$220.19	$220.20	$220.20
Purchase #5	$190.29	13.424%	$215.8345	$215.83	$215.85	$215.80
Purchase #6	$76.61	6.679%	$81.7268	$81.73	$81.75	$81.70
Purchase #7	$219.67	3.206%	$226.7126	$226.71	$226.70	$226.70
7 purchase totals =	$943.74		$1,003.2239	$1,003.23	$1,003.25	$1,003.20