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	$199.25	5.129%	$209.4695	$209.47	$209.45	$209.50
Purchase #2	$102.81	7.682%	$110.7079	$110.71	$110.70	$110.70
Purchase #3	$10.57	13.318%	$11.9777	$11.98	$12.00	$12.00
Purchase #4	$106.67	7.569%	$114.7439	$114.74	$114.75	$114.70
Purchase #5	$29.33	11.498%	$32.7024	$32.70	$32.70	$32.70
Purchase #6	$72.92	8.144%	$78.8586	$78.86	$78.85	$78.90
Purchase #7	$79.41	13.188%	$89.8826	$89.88	$89.90	$89.90
7 purchase totals =	$600.96		$648.3426	$648.34	$648.35	$648.40