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	$89.78	11.195%	$99.8309	$99.83	$99.85	$99.80
Purchase #2	$121.60	3.739%	$126.1466	$126.15	$126.15	$126.10
Purchase #3	$124.36	11.216%	$138.3082	$138.31	$138.30	$138.30
Purchase #4	$163.25	13.397%	$185.1206	$185.12	$185.10	$185.10
Purchase #5	$47.88	6.276%	$50.8849	$50.88	$50.90	$50.90
Purchase #6	$78.46	3.259%	$81.017	$81.02	$81.00	$81.00
Purchase #7	$64.47	13.834%	$73.3888	$73.39	$73.40	$73.40
7 purchase totals =	$689.80		$754.6970	$754.70	$754.70	$754.60