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	$124.65	9.408%	$136.3771	$136.38	$136.40	$136.40
Purchase #2	$95.47	8.794%	$103.8656	$103.87	$103.85	$103.90
Purchase #3	$245.89	11.467%	$274.0862	$274.09	$274.10	$274.10
Purchase #4	$35.48	13.675%	$40.3319	$40.33	$40.35	$40.30
Purchase #5	$144.38	12.764%	$162.8087	$162.81	$162.80	$162.80
Purchase #6	$198.38	3.338%	$205.0019	$205.00	$205.00	$205.00
Purchase #7	$247.64	8.534%	$268.7736	$268.77	$268.75	$268.80
7 purchase totals =	$1,091.89		$1,191.2450	$1,191.25	$1,191.25	$1,191.30