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	$142.42	6.368%	$151.4893	$151.49	$151.50	$151.50
Purchase #2	$75.38	11.172%	$83.8015	$83.80	$83.80	$83.80
Purchase #3	$237.54	10.299%	$262.0042	$262.00	$262.00	$262.00
Purchase #4	$144.71	4.755%	$151.591	$151.59	$151.60	$151.60
Purchase #5	$125.48	4.589%	$131.2383	$131.24	$131.25	$131.20
Purchase #6	$18.64	9.646%	$20.438	$20.44	$20.45	$20.40
Purchase #7	$160.34	6.232%	$170.3324	$170.33	$170.35	$170.30
7 purchase totals =	$904.51		$970.8947	$970.89	$970.95	$970.80