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	$31.57	3.494%	$32.6731	$32.67	$32.65	$32.70
Purchase #2	$40.40	8.543%	$43.8514	$43.85	$43.85	$43.90
Purchase #3	$11.64	10.285%	$12.8372	$12.84	$12.85	$12.80
Purchase #4	$75.69	4.195%	$78.8652	$78.87	$78.85	$78.90
Purchase #5	$187.79	11.309%	$209.0272	$209.03	$209.05	$209.00
Purchase #6	$201.81	8.259%	$218.4775	$218.48	$218.50	$218.50
Purchase #7	$79.63	11.797%	$89.024	$89.02	$89.00	$89.00
7 purchase totals =	$628.53		$684.7556	$684.76	$684.75	$684.80