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	$170.38	11.296%	$189.6261	$189.63	$189.65	$189.60
Purchase #2	$39.55	13.813%	$45.013	$45.01	$45.00	$45.00
Purchase #3	$140.70	12.872%	$158.8109	$158.81	$158.80	$158.80
Purchase #4	$99.71	7.103%	$106.7924	$106.79	$106.80	$106.80
Purchase #5	$162.39	13.496%	$184.3062	$184.31	$184.30	$184.30
Purchase #6	$31.83	10.815%	$35.2724	$35.27	$35.25	$35.30
Purchase #7	$171.40	9.145%	$187.0745	$187.07	$187.05	$187.10
7 purchase totals =	$815.96		$906.8955	$906.89	$906.85	$906.90