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	$53.85	7.537%	$57.9087	$57.91	$57.90	$57.90
Purchase #2	$232.32	6.631%	$247.7251	$247.73	$247.75	$247.70
Purchase #3	$99.90	12.708%	$112.5953	$112.60	$112.60	$112.60
Purchase #4	$250.94	5.207%	$264.0064	$264.01	$264.00	$264.00
Purchase #5	$158.46	13.261%	$179.4734	$179.47	$179.45	$179.50
Purchase #6	$207.91	10.321%	$229.3684	$229.37	$229.35	$229.40
Purchase #7	$139.89	8.872%	$152.301	$152.30	$152.30	$152.30
7 purchase totals =	$1,143.27		$1,243.3783	$1,243.39	$1,243.35	$1,243.40